[bo-n-aro]

Only one thing to do.......... switch him to a lefty.
Over the last 35+ years I have seen many many an archer struggle with this and hands down the ones that switch improved and never went back.
It might take a few weeks to get the "feel" of things and the muscles tunned, but have him hang in there.
I would also suggest you keep him shooting with both eyes opened when he does switch.