Seeing as a lesbian is so different from a transman, I can't really see it as an intermediary "baby step" between straight female and FTM. I suggest going for the truth straight-up, since saying you are a lesbian isn't even a little bit true in your case; it's just another lie you'd have to live. It's hardly better, really just different from the old lie.
And, further, coming out twice isn't very fun. Trust. I personally think just coming out once, and coming out clearly is the best way to go. Obviously, it's your choice, but sometimes (actually, almost always) you have to go outside your comfort zone for at least a short burst to be able to change your life for the better.
Aaaaand, there's also the smaller issue of the fact that you may say you're not attracted to men now, but that often changes as one transitions. You never know. (50 - 60% of the transguys I know are gay, and a lot of them came out as lesbian and insisted they didn't like men before coming out as trans.)
EDIT: I have the annoying habit of going back and editing my posts a lot. Forgive me.