My cousin's barrel horse pawed like crazy when he was tied to the trailer. Her solution was hobbles, the kind that you weave into itself and can adjust, not the chain kind. He could paw (kinda) but it prevented him from going all-out and pawing like crazy.
Now, I'm not saying that that was what I would have done... I think I would work on leaving him tied -- aLOT -- to teach him patience. Tie him while you're cleaning his stall, tie him up and LEAVE him tied up for long periods of time -- not enough to be inhumane, of course, but long enough that he gets the idea that pawing does NOT speed up the process.
That's the best I can do. I'm by no means a professional trainer, so I would definantly consider other folks' opinions!
