While noone in my guild is transexual as far as I know, we have had several come out as gay.
My recommendation is to just stop hiding it. Slip something in a conversation. That's how i've seen gay guys do it before. "Can't come to raid next Thursday, me and boyfriend is going to the movies". Very few reactions ("Did you say boyfriend? Didn't know you were gay. What movie? Transformers sucked"). Not sure how you would slip in something that reveal that you are transsexual, and I suspect any suggestion I could come up with would sound bigoted and ignorant, so I will leave that up to you.
If you act like it's all natural and no big deal, most people will just go with it. In many cases, people may very well think that you have been open about it all along, and that they just never cought it.
If you make a big deal out of it, so will others. If you don't, neither will others. Bigots will always exist, but unless you are in a really bad and unpleasant guild, they will know very well that their opinions are not accepted and just keep their mouths shut.