Well, I think I'm the guy you're talking about or at least a guy in a really similar position to the one you mentioned. The similarities are uncanny.

You're not shallow. I think physical attraction is a must for both people and I would never want to date someone that's not physically attracted to me. Just because you are not romantically interested in him doesn't mean you two can't be good friends. The problem is it's really hard to friend zone him and be very clear about it so that he doesn't have a false sense of hope. It's not something that you'll just mention out of the blue. If I were in his position, I would want to know that it was my looks that's holding me back. His feelings are going to be hurt no matter what because he's losing you romantically. At least being honest with him will give him some peace of mind otherwise he'll be spending days trying to hypothesize where he went wrong. Maybe a statement like, "you're just not my type and I can't see it every working out as a result" is the best euphemism for your situation.

So if there's something you'd like to tell me, now's a good time hehe.