A good friend of mine became a pastor. We discussed this issue some years ago.
He said a number of pastors in his city agree that if the govt forced churches to marry same sex couples, then the churches would declare they would no longer perform marriages. Marriage would be civil only.
The church would then perform a "blessing," it would look like a marriage. feel like a marriage, have all the trappings of a marriage...BUT it would be open only to church members-not to people walking in off the street. further the church would have the freedom not to give a "blessing to anyone who did not meet the churchs rigorous standards.
--since a "blessing" is a religious only event, the govt could not do a thing about it.