Where is he feeling the recoil? Is he getting slapped in the face, or getting a sore shoulder and /or headache.
If it's face slap then the first thing to do is look at gun fit. As Sitka suggested, reduce/remove cast by inserting a shim on the right hand side (for a right handed shooter).
Also look at reducing pitch by shiming the bottom of the recoil pad. Try to head towards neutral pitch (the pad at right angles to the barrel). It's probably got down pitch at the moment (put the pad against a wall and you will probably see that the barrel points down).
If it's plain out recoil (sore shoulder, aching neck, headache) then your only real options are increase the weight of the gun or (easiest) reduce the load (see gnoahhh's advice above)
