If he's straight, but you two get on, then he'll be up for something. But, the issue might be privacy -he would need to be reassured that you won't go talking to other people about him, not just in relation to sex, but that you're a mature, trusted friend in general. Then, you can have some fun, but don't expect him to be into it --it'll just be a curiosity thing, or a dare. If you want to approach him to talk about feelings etc., that's tricky and might well not be very productive. The first thing to realise is that your relationship is going to be limited. Think about it a while. You might need to disengage emotionally. If you play it cool, he's not going anywhere... so sit back, be collected, and figure out what the limits are, what would be good for you and good for him. With that attitude, I hope you'll find him receptive to a little advance. If you're kind of hung up on him, it seems like it's all about him, but remember to consider yourself, what you're feeling, why you're feeling it, etc. So introspect about overall feelings not just those feeling that are about him.
It's complicated! Sometimes it's just better not to analyse so such (at least not all of the time) and be spontaneous. Come what may...