Give him plenty of time floating in water - deep enough for floating but not drowning if he gets tired, you may need to watch. And you may want to limit his food intake - more vegetables in his diet to keep him full. This is a tough one. But I wonder if you can help him lose a little weight.
Also, you may want to make him a sling on a frame with wheels - a scooter of some sort.
Also, you may want to make him a sling on a frame with wheels - a scooter of some sort.