Well, let's see... church is a lot like a workplace in many ways. When I came out as gay a few years ago, all I had to do was tell one person and everyone knew by the end of the day. It was a very efficient "coming out" for me. Of course, a bit piece in The Advocate and a letter supporting same-sex marriage in the local paper in the same week didn't hurt either...
My thought would be to talk to some of the leadership in the LGBT group. Once you're all on the same page, you can come out to the entire congregation.
Even though your transsexuality is "no secret" to the LGBT group, I think a formal "coming out" would be appropriate.. especially to the LGBT group eventually. They can celebrate with you at that point.
Like I said, then they can support you when you feel it's appropriate to announce to everyone. Susan is sitting here (our weekly Friday night gathering, of course) and suggests even having a handout available with some basic information about transsexuality and how it relates to the Scriptures. I agree with her.
But that's just my thoughts... get your allies together, PRAY, PRAY, and then PRAY some more... then go for it when you have that peace in your spirit.
Praying for you,
David