Now, I don't know a thing about this kind of thing at all - I'm a bit of an idiot when it comes to this, but here's my twopenneth anyhow/what I might try doing if I was in your situation. I have no guarantee it's the right thing to do whatsoever, it's just probably what I'd do.
Basically, I think it depends on how well you know this guy. If you don't know him all that well, you could from his perspective be just another girl trying to flirt with him if you try that approach. By the sound of what you're saying, he basically just flirts back when girls flirt with him - so you never know, it could be refreshing for him not to have to put it up like that for someone. If you get to know him a bit more, it might give you some clues as to how to progress.
If you know him reasonable well - I'd just try and build on whatever you've allready got. So if you're good friends, spend time with him and try and show him you care etc.
As an aside (and I have tried this - it didn't quite work in my case...) if you think it'd be effective, it could be worth just taking him aside and just telling him directly that you like him. That way he doesn't have to flirt/pussyfoot around the issue, he's just got the fact right there in front of him. On the other hand, though, I'd say this approach is normally worth trying only with people you're sure you can trust. It's also very, very difficult to get the courage up to do it and if the person can take it or leave it you need to be prepared for the possibility they might leave it. It's just a thought though.