I am currently dealing with rehabing an injury and I can give you some of the tips im using. Get MK-677 and take 10-20mg daily for added GH and IGF-1. If he can get boldenone, get boldenone. Transdermal BNE if possible, around 400-500mg a week is what has been proven to aid with this kind of stuff. Tren is a little on the harsher side and probably not necessary for a fracture recovery. If anything id replace the tren for boldenone and lower the test dose. Additionally, and this is whats been giving me the best recovery so far, get BPC-157 AND TB-500. inject BPC-157 directly next to the affected area, TB-500 is more systemic but will probably help.
Other than that, resting the broken arm is the way to go, dont do anything that uses that limb at all. What does help is doing any other exercises that are doable. For example: assisted squats, HIIT, lunges and any other exercises he can perform without causing any pain to his arm. Oh and LOWER THE WEIGHT. He needs to accept right now that he will be using bitch weights until he can be sure he can raise the weight without risking the use of his arm for stabilization or whatever. You want to add anabolic signals coursing through your body without beating on the broken area for maximum healing potential.