Another thing you might try is a small mesh hay net. I haven't tried it myself yet, though I plan to start immediately when I move my boy into the barn in a few days, but I've heard it helps get rid of feeding time anxiety.
The smaller holes in the netting don't allow the horse to bolt the hay. Instead, the horse has to slow down which encourages constant grazing so the horse isn't starving when feeding time comes. It's a more natural way to feed and also prevents ulcers by keeping their tummy from being empty between feedings.
Just something to try but definitely take the training advice from above as well. It's VERY important that you and your horse have a mutual respect of each other and that he understands that YOU are the leader. It will make things much safer for both of you! Good luck :)