You know, I've wondered about this sort of random not-so-passing thing... especially considering that at the moment, I'm living in the small town where I went to high school, and everyone here always knew me as female.
Really, the best solution I've come up with is just not to say anything. That said, I tend to avoid the places where I know people will call me "ma'am" or call me by my birth name. The really funny thing to me is, people I knew for 10 years now look at me and don't recognize me, and call me "sir." Those who do recognize me don't say my birth name... they're just like, "Oh hi, you, I haven't seen you in awhile!"
Depending on what type of people the folks at your cafe are, there are a couple routes to take, as I see it. If they're very nice and understanding, I'd say you probably ought to just pick a time when they're not too busy to explain that you're transitioning to male, and their calling you "ma'am," etc., is embarrassing. If they're not, I'd say either avoid the place, or do what others have suggested: just try to be as masculine as possible, and hopefully they'll get the point.
SD