A simple answer already exists and has been in use in the UK for 8 years now. There is a 'conscience clause' that was included in the Gender Recognition Act 2004, which allowed religious organisations the choice as to whether they were willing to perform the marriage of a transsexual person (who had obtained legal recognition in their new gender role) and their partner.
As it happens, in 2005 when the Gender Recognition Act 2004 came into force, lots and lots of trans people married their partners that summer. A very large number of those couples married in churches, in the full knowledge of the minister who married them, and often in the full knowledge of the congregation - as did my partner, Sarah and I.
We had originally intended to have a registry office wedding. We had attended a small methodist church by then for about 12 years. We went with our children, primarily to inoculate them against ever becoming born again, but also to give them a religious education whereby when they later sang church music or read poems, or listened to Bach's Requiem, they would have some understanding of the nature of sacrifice. The plot worked wonderfully, they are good cynics but with a strong sense of what is right or wrong, and a better understanding of the human tragedy than most.
We also found that hour on Sunday morning in which we had both a quiet space to think about our obligations to the world and the people in it, and then a loud space in which to sing our hearts out as a community, a really robust and worthwhile contribution to our otherwise very busy lives.
The church council, at our request and after a meeting with Sarah in which she had explained what the Gender Recognition Act would mean, and why they should give it their backing, had written a letter to the Government to support the intention to bring in the Gender Recognition Act. We were grateful that they had taken what was a very difficult issue for some of them, and had taken the time to read and learn about how our human rights were contravened. When the Act came into force, the church minister came to visit and say that if we were planning to get married, as a church they would be extremely happy to host our wedding.
We couldn't say no to this offer, knowing how many of the church had put in an awful lot of thought and effort to support the Act.
In June 2005, over 180 friends, family and church members enjoyed the most wonderful day, celebrating not just our wedding but the strength of a relationship of 2 people who had gone through hell and high-water to be together, who had raised 4 wonderful children, and who were still together 26 years later. (as we now are 34 years later).
Eight years later, looking back I think of hundreds of couples, where one is known to be trans, who have married in churches, which have very happily accommodated them. Equally many have married in a registry office.
In the context and discussion around same sex marriages, and extremely important in the discussion must be the recognition, that as the Gender Recognition Act does not require trans people to have undergone genital reconstruction surgery, many of those marriages, whilst of 2 people with different genders, will have included 2 people who either both have a vagina or both have a penis. In other words, same sex (but different gender) marriages have been going on for 8 years now.
And the sky has not fallen down!!!
Examples of how the Gender Recognition Act 2004 has led to same gender or same genital marriages legally taking place for the last 8 years.
(all images are copyright 2013 Stephen Whittle, if you want to use them please contact me directly and ask permission)
(all images are copyright 2013 Stephen Whittle, if you want to use them please contact me directly and ask permission)