Unless you are willing to go to extremes (twitch, lip chain, etc.) and deal with any behavioral reprocussions to try and MAYBE get him to take an oral tranq I'd call the vet. Basically, if you want to save the horse, your going to need to call the vet for now. Sorry, to be blunt, but I've seen horses get put-down for lesser injuries in that spot because in wasn't taken care of properly (not saying your not trying to do the right thing, just checking out your options)
The only other non-vet thing MIGHT be to hobble and restrain the other leg so the horse can't go anywhere. BUT, ONLY if you ABSOLUTELY, POSSITIVELY, WITHOUT A DOUBT
know what you are doing and experienced with doing both and have others with you with just as much experience. The ONLY person I've ever seen do it was a 68 yr old lady that was born on a horse, grew up on a horse, slept on a horse. So basically she knew what she was doing.