Get your husband to go have a word? :P Ok, I actually know that's not an ideal solution. Gosh, what a tricky one. I'll go think about it and come back if anything pops up! I hope someone comes along with some sort of reasonable solution though. That sounds terribly awkward.
Maybe you could try talking to him one last time. Letting him know that you'd like him to stop for the sake of the friendship... thing is, because you've already told him that you want him to stop before and because he does it without even realising it sounds like part of who he is. Maybe it comes down to you either putting up with it (if he doesn't respond when you speak to him) or taking a step back from the friendship.