I wouldn’t do this. My advice is to stay away and keep things on a friendly basis.
But if you must, then take him out to a bar or a party and get him pretty drunk. So drunk you have to walk it off before you get in the car. Then as you are walking around, find some dark place where you can bump into him or hold onto him for support, and then, at a proper moment, if it seems like he might be receptive, pull him into a sort of embrace, nuzzling his neck.
Now it’s possible that he will be so drunk that his inhibitions are gone and he responds, but then in the light of sobriety, he is all embarrassed and he pulls away and acts all weird towards you from then on. He might step back and punch you out right then and there. Or he might give in, and it turns out later he had the hots for you, too.
You could precede this with a general conversation about what a raw deal gay men get in our society, just to see what he says. You might bring the conversation around to the boy scouts. See if he’d ever been in them. If so, see if anything ever happened. You might share your own “boy scout” story, just to see if that opens him up.
If he seems to have a “boy scout” story, then maybe the action, later on, will go well.
But as I said, I think you should leave him alone. He’s your roommate. If you make an approach and he rejects you, your living situation will be hell until one of you moves out. Guess who is going to have to move out?