I think the bucket idea to try to heal him back is the best idea offered here.
Unless you can find clove oil, or unless you have the nerve to chop his head off with a scalpel or sharp pointed object to put him out of his misery, I'd really try the bucket approach. If he's hung on as long as he has in that condition, he's obviously a fighter and deserves the chance to at least decide when it's his time to go.
I didn't mean to sound like I was criticizing earlier - it just sounded like you were desperate for help and didn't realize that the barbs would surely nip the heck out of an angel when put together. If the angels were both sick when you got them, and the other one died, and if this one was still sick that's all the more reason for him to get picked on.
Good luck.