I know the shoulder limitations well.
Some possible ideas:
- Go to a lower density bullets - such as copper. There are good ones from GS Custom, Cutting Edge, and Barnes. It should be possible to get down to a 120 - 130 grain bullet, which also helps.
- If he needs something to really go light with, there is a flake powder used in cowboy action shooting that can take about any round down to the 1500 fps range with a full case. I need to think about the name of it.
- A prior poster mentioned placing a towel between the stock and shoulder - great idea. I have been known to use my wallet in a pinch. Maybe shorten the stock and put in a really thick recoil pad.
A harder option, but he might consider to change shoulders.