Personally, I would try the hand method mentioned earlier before the rope method. From your description he threatens more from ignorance then meanness. Take the time to get him used to being touched everywhere
with it, then when he calms about having his legs touched with it, start working your way back there with your hands. Take your time and work in an approach/retreat methodology. Gradually work your way back there and down his legs. Making sure to retreat before he can react with a threat. Just go a little farther each time before retreating.
I understand that you can only get to the barn on weekends, but this is really something that needs to done daily for a while until he is comfortable with having his rear legs handled and his feet picked/trimmed or whatever done to them.
You also mentioned that he does not like to be brushed behind the rib cage with even the softest brush, but does not mind if you touch him with your hand. Have you ever thought that maybe his skin is most sensitive there and that is why he doesn't appreciate being brushed there. Just a thought, about something that stuck out to me in your original post.