When he holds his grudge, can you put him in a stall where you can more easily catch him? Leave a halter on him with a short rope (about 12-18") attached. Make sure the halter is well fitting so he can't get a foot caught in it.
I still wish there as a good trainer nearby. It doesn't need to be a miniature trainer, a good big horse trainer would do.
I would probably put him in a stall and remove him from his other horse buddies so he has no choice but to turn to you (or another person you trust) for company.
By leaving him alone when he holds his grudge, you are actually giving him what he wants - which is to be left alone. He needs to learn that he must have manners and that he will have to submit to being handled daily. In exchange he will receive food, water, and eventually he'll enjoy the love you give him.
So when he nips, pop him with the chain and then continue petting, grooming, etc. So he learns that nipping will be corrected and he still needs to put up with being handled.