Tough one. I would bring up smelling amazing in casual conversation with him. Like, say, "Hey Joe (or whatever), how is your wife/kids? Notice how great I smell? I utilize (insert body wash/deod./cologne/product of choice) to maintain my great'smelling'ness. How about you?" Then he will realize that smelling great means something to you and may have a little more self respect.
this is probably better than my idea, I was going to casually spray him as he was walking away with some good smelling cologne or body spray.
the odd thing is no one else has brought it up and its too often and too long of a smell to be farts. may need to investigate his shoes

I'm desperate may have to re arrange my hallway walking to avoid contact w/ him.
afraid I may say something mean/embarass him and I'm not a mean guy.
Smell is a pretty touchy subject ppl really take it personally when you think they stink and they don't think they smell.