Doesn't sound very appealing to me. A large part of the turn on of blowjobs for me is visual. I like to see what's happening. Plus I like to touch the girl. I don't think the wall is going to look as sexy and it's certainly not going to feel as soft.
Aside from all of that, my imagination is too vivid. if I stuck my dick through a hole I'd imagine a chick lighting a match under it or sticking it into a shredder or something. I don't think I could stay hard. Maybe I just never learned to trust
