How would Reformed Christians deal with homosexual marriage of individuals prior to their conversion to Christianity? I've been pondering this for several weeks and I believe that the reformed church (really, the church in general) is woefully unprepared to answer the following question:

How would the church deal with a gay couple that were not Christians when married, that then become Christians?

Specifically when we have passages like 1 Corinthians 7:17 (NIV)


  17 Nevertheless, each person should live as a believer in whatever situation the Lord has assigned to them, just as God has called them. This is the rule I lay down in all the churches.


I'm looking for relevant biblical quotations, relevant quotes from reformed scholars past and present, and any statements by reformed churches or denominations that have come out in recent years. 

I'm also interested in how circumstances and views change when 1 partner becomes a Christian, when there are children involved, and when both partners become Christians.

As gay marriage becomes more prominent, legal and prolific in our society, questions like this are going to be more and more relevant and the Church must be prepared to deal with an answer these queries.

I'm specifically interested in reformed sources here as they are most relevant to me, but I would be open to other sources that take a similar view of homosexuality.
John Piper addressed a portion of this question in the context of Minnesota's "Same-Sex Marriage Amendment".  Having listened to his sermons on Romans 1 and other statements by him, the following principles are his consistent teaching on the question:


  
  Marriage is created and defined by God in the Scriptures as the sexual and covenantal union of a man and a woman in life-long allegiance to each other alone, as husband and wife, with a view to displaying Christ’s covenant relationship to his blood-bought church.
  There is no such thing as so-called same-sex marriage, and it would be wise not to call it that.
  Same sex desires and same sex orientation are part of our broken and disordered sexuality owing to God’s subjection of the created order to futility because of man’s sin.
  Therefore, same-sex intercourse, not same-sex desire is the focus of Paul’s condemnation when he threatens exclusion from the kingdom of God.
  Therefore, it would contradict love and contradict the gospel of Jesus to approve homosexual practice, whether by silence, or by endorsing so-called same-sex marriage, or by affirming the Christian ordination of practicing homosexuals.
  The good news of Jesus is that God saves heterosexual sinners and homosexual sinners who trust Jesus, by counting them righteous because of Christ, and by helping them through his Spirit to live lives pleasing to him in their disordered brokenness.
  


I extracted these from the text of his June 16, 2012 sermon, but left off the last two points that shifted to the Church's attitude toward political action.  Piper obliquely addressed the question of what to do if members of this sort of union were to join his congregation:


  Churches will be faced with new and unheard of cases of discipline. Suppose two so-called “married” men hear the gospel and one of them believes and comes to your church. Will you council “divorce” and moving out?


He also quoted 1st Peter 2:12's encouragement to engage the world with honor:


  Keep your conduct among the Gentiles honorable, so that when they speak against you as evildoers, they may see your good deeds and glorify God on the day of visitation. (ESV)




I believe we can extrapolate from these principles:


Like any other sin, homosexual practice should be resisted.  If a new believer continues in their habitual sin, it's the responsibility of the Church warn against the dangers of sin.
On the other hand, homosexual desire is like any other temptation.  We should not be afraid of it.  Christians resist temptation with the power of the Holy Spirit.
Same-sex marriage is not binding in the eyes of God and nor should it be binding in the eyes of the church.  


So we can safely ignore the teachings on divorce in this case; divorce as understood in the Bible just doesn't apply.  Instead, I think the actual parallel is to the state of voluntary servitude.  That analogy might seem distasteful, but in the Roman world being a bondservant was actually a respectable position.  Many bondservants performed duties that we would recognize as white-collar professions.  More to the point, it was a civic obligation that Paul explained was no longer binding to believers.

Here is Paul's advice:


  Were you a bondservant when called? Do not be concerned about it. (But if you can gain your freedom, avail yourself of the opportunity.) For he who was called in the Lord as a bondservant is a freedman of the Lord. Likewise he who was free when called is a bondservant of Christ.&mdash;1st Corinthians 7:21-22 (ESV)


Therefore, it seems to me that a Christian who submitted to a same-sex civic contract before they converted should abstain from sexual intercourse, but honor the other obligations of the union.  That would include financial and parental duties if applicable.  Separation should be seriously considered in order to reduce temptation.  If there is an honorable way to nullify the union, that should be pursued.  If not, nobody should be concerned about it.

Conclusion

It's very likely we will see some missteps and controversy in the next generation.  Our society is increasingly approving of same-sex practice, but the church should not be.  I'll let Piper have the final word:


  One of the most powerful things we can do is fold into our churches men and women who have same-sex attraction and surround them with a bigger vision of life and love and relationships that make it possible for them to flourish in families and friendships. These stories may be one of the most authenticating messages for the Christian gospel.