Need suggestions for stopping play aggression in a previously feral cat...

I have a "previously feral" foster cat, and it took about a month and half to gain his trust. I have worked hard, and he has come a long way. If a human does something offensive to him, then he still quickly becomes frightened and will run away.

There are times when I'll be petting him and then he gets that "wild" look in his eyes like he wants to play, and then he bites me. It's nothing awful, he just kind of places his teeth on my hand, he has never broken skin. I pull my hand away and then ignore him, but it doesn't seem to be working.

How can I train him to stop this behavior without doing something that will frighten him? I read in a stickied thread at the top of this page that blowing in their face or clapping your hands loudly is a good way to reprimand a cat for play-aggressive behavior. But is this a suitable method for a previous feral? I'm afraid I'll lose his trust slowly if I start this method of correction with him.

I also read a little about clicker-training...would this work in his situation? When would I make the click? When he's letting me pet him nicely? It's kind of hard to pinpoint that certain action.

Thanks for your help!