Short answer...you can't. Long answer...you can't not.
There are some tenets of postmodernism that simply run contrary to the gospel. The biggest of these is what is known as the death of the metanarrative. The metanarrative is the one over-arching story which gives meaning to all humanity. For Christians, this story is the gospel, as recorded in the Bible. For a person to say that there are many stories which give meaning to all humanity they would need to deny historical orthodoxy. The story does have many expressions, but there is only on mediator between God and man, His Son, Jesus Christ.
Sidebar: it is just as easy to find problems with a modernist worldview that would make it impossible to be a modern christian. i won't argue those here because this part of the discussion is useless beyond preamble in this context.
At the same time, however, there are several characteristics of postmodernism that Christians can embrace. George Cladis, in his book, Leading the Team Based Church (an obscure resource for postmodern thought...) gives 9 characteristics of postmodernism that Christians can embrace, and, perhaps, become thereby more effective. I will interact with these here:
1. Creation is an organism rather than a machine: In the modern era there has been a lot of effort put into controlling nature. It's exciting to us that we can predict earthquakes, tornadoes and hurricanes. It's even more exciting that we are developing scientific means by which we can eliminate these natural disasters, or at least make them happen in ways and places that are less destructive to our societies. We wanted to set up a hierarchy where nature was under man and at mankind's disposal. In postmodernism, nature is seen in a relational way. The reason that those natural occurrences are disasters must have something to do with our relationships with nature. Putting New Orleans below sea level was an economic decision - it was worth the risk for the monetary benefit. The levees were built so more sea faring vessels could port there and it became a disaster when they didn't work. Could it be that the natural disaster is really the way that we have let things other than relationships dictate our involvement with the natural world? This is an advantage of postmodern thought.
2. Hierarchical structures are reduced: In a postmodern culture there is a lot of value in innovation. New discoveries excite people. In a church that is stuck in hierarchy, all the new ideas are the ones thought of, or approved by, the highest level of leadership. Thus, innovation is stifled. Further, hierarchical structures deny the gospel as they resist the greatest becoming the least and the highest serving the lowest. In short...hierarchy can quickly kill the gospel; the gospel is flat.
3. Authority is based on trust: Remarkably, years and years of education do not make better pastors. I love that we think this is a new discovery! Look at the disciples, they were not the most highly educated folks - but they had massive amounts of authority in the beginning to the early church (and still do today). I really don't care what position you hold, I'm not following you if I don't trust you. I want leaders that lead from their hearts, not from their degrees and training. I want leaders who lead from their convictions, not from the latest business or leadership book they've written. Tell me the truth, show me empathy, expose the kinks in your armor or else you'll find your leading nobody to a land that no longer exists.
4. Effective Leadership is Visionary: In the modern world managers motivate through job descritpions and threats with a paycheck. There was a position description and units of production were delineated, with monetary rewards and consequences. In the postmodern world money is not enough and threats are poor motivation. Motivation must come from vision and heart potential. Leaders must help people see the importance of their work. Church leaders, then, must respond to the prophetic voice that God has placed within them and cast a vision of the future that is hopeful (and therefore attractive) and help people contribute towards that vision.
5. Life and work are spiritually rooted: In the modern world, your life was what happened outside of work. Today, in the age of Ralph Nader and Coupland's J-pod and Microserfs work is your life. In the same way, a job is no longer secular and life is sacred; rather, all becomes spiritual and people seek the sacred. I don't think argument is even required here. Instead, I think Christians in postmodernity have opportunities for christian spirituality in the workplace. Discussion groups, lunch gatherings, book groups are all effective ways to engage the spiritual people around you. People want God...if you know where he is you could at least share that information!
6. Structures are smaller; networks are bigger: While some would think that this shows the leftist tendencies of postmodernism, I think, again, it's more of a small business/organization leadership principle. A great example of this takes place in the youth ministry here at SACC. Over the past couple years we have employed former prostitutes in Calcutta, sent $17,000 to fight world hunger, bought 3 goats and 24 chickens for a family in Peru, freed fetish slaves in Ghana, brought joy to a soldier in Iraq and got active in Compton (including 22 salivations), Pasadena, New Orleans, Vancouver and San Francisco. We are a regular old youth ministry in Albany that has a network that extends our influence worldwide while remaining very lean, organizationally, here.
Further, postmoderns have a general distrust of bureaucracies and favor extremely broad networks. This is influencing the way denominations have to operate. There is less and less volunteer submission to denominational authorities because they 'don't know us.' This is even evident, I believe, in a local mega-church pastor's public comments that his church no longer 'needs' the denomination. While this pastor cries out the evils of postmodernism, he reveals his own temptations against denominational leaderhsip, revealing a postmodern influence in his own life.
7. Innovation is rewarded: The best ideas come from the trenches. A general in an air-conditioned office has no idea about the efficiency of a shovel. In the postmodern world, the general who knows how to listen and adapt will be the most effective. We no longer need people to convince us of the vision, we need leaders who can detect the vision put within the priesthood of the believers, and call it out for us. we need leaders who can name the vision that we already have!
This is especially interesting to me considering the emergent church. In the past success or failure has been based on church survivorship, or, even better, growth. That was when we all were asking, "What does church look like?" Now, at least in my denomination, leaders are wanting to ask, "What could church look like?" The problem comes, however when the two questions are answered with the same metrics. In the former question we value success, perfection, achievement of a model. In the latter, we value, exploration, experimentation and have to live with the reality of a failed experiment. If Edison were trying to invent a light bulb in the modern church his program would have been shut down after so many failures. In the postmodern church, his explorations would have been celebrated regardless of success.
8. Work follows gifts, and gifts are used collaboratively: In the modern world the work of Christianity was done out of a sense of duty and obligation. Today, we have an opportunity to enable people to consider their gifts and talents and help them to find themselves contributing to the gospel in ways that they can see God using them best. No longer do we need to enlist megapeople to a megaprogram. In a relational network era, we can avoid needing people to fill spots and instead create ministries that match people.
9. Mainline church domination has ended: This is one effect of the seeker-sensitive/purpose driven model. While those are great in and of themselves, they have widely been received as the only way to 'do' church (Even the fact that we have a saying like 'do church' is alarming). Further, this is a wild westernization of postmodern theory. Mainline churches are now historical centers all over Europe and we are quickly heading the same way in the new world. I think this is wildly sad because it is happening for, I perceive, two reasons. First, mainline loyalty is over and done with. If I were to move to another city, I would not ask, "Where is there a ________ church?" I would, instead, ask, "Where is there a meaningful church?" People are no longer dividing themselves theologically and denominations are just not getting this as they continue to argue over there distinctives. Secondly, this is happening because of what sociologists call the circulation of the saints. Churches with older people and older leadership are having a killer time relating to the young and so the young are leaving to go to the church that has meaning for them. Yet, nobody is calling out these young people for being lazy. I will! I think the mainline church (heck any stagnant church) can grow if the young people roll up their sleeves and do the work that it will take to turn the tide. I desperately pray that the young will stop letting the boomers do all the work for them and that they would act like the church of today. Youth pastors always say that the youth are the church of today, not just tomorrow. I say that if the church of today (youth) don't start taking responsibility and involving themselves then they will quickly turn into the church of nothing happening. If you are a young person stop being so satisfied with your life - CHANGE EVERYTHING!! Today the postmoderns are crying for collaborative leadership - mainline denominations are best equipped with old folks with resources to make this happen.
May God be faithful!
Addendum: This post took me two weeks to write. Comment!!