Depending on the medical restrictions; light duty at my store usually means cashier, guest service or fitting room. I've never heard of someone in flow being on light duty, there's nothing light about flow.
There actually is a lot that you can do on flow with medical restrictions. Throwing the truck and lifting heavy furniture are obviously out but you can do the parts of the process that others have mentioned in this thread. You could also collect the cardboard though making the bales would have to be done by others. If they're unable to participate in the unload process, they could help zone.
People on medical restrictions could also do certain pulls and backstocking in the backroom, like the open stock merchandise in the wacos. No heavy lifting involved and no bending over or climbing ladders.
Unfortunately he won't do any of that.