Hmm, I wouldn't take the polite approach. I think, it may seem too personal and the person may be more offended/embarassed!

I think, best way is, straight out, jokingly, say it, that he is stinking! I won't give an example, but I guess you know what I mean. Do it in a non-serious/joking way, the message will get through to him and due to its humerous nature - no one really is going to take it personally.