A lot of couples go through this. As always, things in the bedroom are a matter of communication, even if some people don't seem to think so. Before you do anything in bed just lie back in bed and ask him if he'd do it for you since after all you do it for him. If he says he doesn't like to than ask him why. Try to communicate, if he's got valid reasons for not wanting to than see if you can compromise a little. Even ask him to try it before he completely disregards it. Some guys don't do it because they're actually afraid to, or because they think they're no good at it from experience with someone else.
There's a ton of reasons guys don't do it, personal hygeine is one of those things but it's not all of it. Some guys are different, some have different concerns. Talk about it, maybe if you can get him to try it than he'll see its not that bad. If he tries and still doesn't like it I suppose there's not much you can do in that case.
Really though, try talking about it. It's not really a matter of convincing, it's really just a matter of talking, since you can't convince a person if you don't know why they won't do it.