If you feel safe with him, and feel confident he's not going to freak out, then I would approach it differently. When you first get to the room, and you're just relaxing on the beds, I would just say, "Feel free to jack off if you need to." If he says nothing or "no thanks" or something, I would just add, "I mean you don't have to hide it or wait until I'm asleep or anything. Just jack off like a man. Right here, I don't care. I might later."
At least you will have started to create an air of permissiveness. And when you shower, strip nude right in front of him before going in, and come right out nude and don't hide anything. That will let him think your attitude about nudity is very casual and he may feel like being nude around you. Then after planting these clues by your words and actions, he may feel more casual about all this, and maybe more open-minded about some kind of activity, even if it's just jacking off. Even if he is not attracted to you sexually, he still may enjoy the camaraderie of jacking off together as a "guy thing."
And later, if the timing is right, you might just say, "I need to jack off." And just start doing it, right there on the bed. Don't ask his permission or anything. If he tries to leave just say, "Oh that's cool you don't need to go." And then continue. Your act of doing it might trigger some horniness in him. And who knows, he might even jack himself. Wouldn't it be more fun to you to watch him jack off nude, than to just smell his underwear?
Depending on how he reacts to all this, you could offer other suggestions, like "let's take a shower." And if he agrees to shower together, then that's your golden opportunity to soap him up and feel his body.
Or if he is jacking off and seems to be in "the zone," then maybe even, "let me suck you." Don't phrase them as yes/no questions that he can answer "no" to. Phrase them as suggestions. He can either respond or not respond, but the suggestion will plant an idea in his head.
Again, all of this depends on how he reacts, and if he reacts negatively at any point, you had better just drop the whole thing. But if he reacts positively or says nothing, then you know he's cool with it. A friend once told me, "Anything is allowed until they say 'no.'" How far you want to take it will be up to you; maybe it's better not to push it too far and try to get actual contact with him. But, if he strikes out with the girls and ends up back in the hotel room horny with you, well then... make a suggestion. "Let me suck you off." He will probably just laugh. "No, really, you're hot. I want to." Don't bring up gay, bi, straight, any discussion. Just "Let me suck you off." He'll either say yes or no, depending on how horny he is and how safe he feels with you.
But if he is homophobic, even a little bit, none of this is going to happen and it's going to remain forever as your fantasy. And you're going to be left with nothing, except smelling his underwear.
