I would add the stabilized rice bran, as directed, and 3 pounds a feeding of beet pulp. We always fed the beet pulp dry so it expands after the eat and drink, either will work. As long as he cleans all his feed up I would get him on free choice hay as well, you need to expand his guts to get the flank to drop.
By now you should have decreased his protein intake and increased his fat, the stabilized rice bran will help do that.