Whenever I feel like crying, I try to laugh. Even maniacally sometimes.
Then I genuinely laugh at myself for trying to laugh, and it'll leave a smile on my face, a true smile.
Anyway, you should try something like that. Just let go of yourself and act completely crazy for a while. In the end, it'll either leave you smiling or it won't have done anything. Either way, no harm done.
I've been smiling a little more lately. It's a weird experience. First the right side of my face bulges and budges up just a smudge and the left side starts up just not to be left out. At long intervals, my mouth drops open and I find myself laughing; sometimes at a joke. Sometimes because orange is a good color but not on a Corvette. Hey. So that's how people (them) smile? I bet it hurts like crazy to do this all the time; I don't see how.