Be consistent with your "signs" that you like him - most guys will convince themselves that a girl is not attracted to them, and that any signs are just being misinterpreted or mere affection, which is why girls tend to complain that guys don't ge the "hints", so I would ensure that you come across in a way that cannot be interpreted in any other, although it doesn't mean you have to be obvious.
I'm afraid us lads aren't mind readers..in fact half of the time, we aren't even very bright when it comes to things like this. The only way to let him know is to bite the bullet and come out with it..
I'm gonna let any girl who dosen't know this but most guys would nver turn down a girl especially if there is sex involved...just make it blatantly obvious you like him...if you want to fanny about with some games and hints, it might be fun , but it willl get you absolutely nowhere...
The most obvious would be telling him, or making obvious signals such as constantly touching him, etc. I have seen people interested/flirt with me, but only on a very superficial level, maybe due to looks/body language/whatever, but it soons disappears, showing that flirting often means little (or that you are different from their expectations).