Have you tried tying him with a bungee tie (with supervision) while he's eating? That would be the next thing I tried. And if he still tried to pace, I'd hold him on a lead line from outside the stall and give him a sharp & very loud HEY & handclap each time he went to move away from his feed bucket to pace/weave. Probably along with a good tug on the lead rope. It can help a lot to snap them out of their learned behaviours and overlay their experience with something else.

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