hey, I'm new too--gonna continue the trend here.
did you know that the number one reason people said they ventured out and 'asked out' their gf/bf was because they thought he or she liked them back? speaking as a (sometimes rather apologetic) member of the male species, the easiest thing you can do is drop a few hints, maybe let the rumor float out to him. after all, they things holding you back from straight out telling him can probably be summarized as 1: not wanting to ruin your current relationship and 2: fear of rejection
so, let him know via gossip/things you do, but don't verbalize it unless you're ready to take that leap--when it's spoken out there, you won't be able to take it back. unless he's really really REALLY shy, he'll take the bait if he likes you. if not--maybe he doesn't want to be more than friends. in which case you listen to a lot of sad music, watch chick flicks, and move one, move on, move on