He could use a replaceable blade model, with a TroCar tip. Something three blade maximum and narrow cutting diameter. No more than 1 1/8" should do nicely. I like the InnerLoc heads, maybe in 75gr or 85gr. Then there the Wasp SST Hammer in 75gr also. Muzzy makes a few that are 1" cut.

And the other trick is to limit the range he is shooting. Maybe a max of 25 yards or so, depending on his accuracy.