I assume it's the Mossberg Bantam, sized for smaller shooters. That's a great starting point. Let's see, the gun has a rubber recoil pad (but perhaps could be softer?) and has decent weight. If you're already using target loads of 7/8 oz, that gun shouldn't be kicking the crap out of him. Perhaps we could analyse his stance and how he's holding the gun. Any pictures of him shooting it?
If it turns out he's getting full contact inboard of his shoulder and leaning slightly into the recoil, you could consider making your own lighter shells with 3/4 oz. of shot.