I didnt have a trapped ulnar nerve but a "flicking/twitching" ulnar nerve (perma elbow pain and lots of electric shock type pains with movement)- which the brill shoulder physio at stanmore had dxed and had told me "pity enough there are no exercises that will help this- you could try an op to move the nerve to the inside of the elbow"
BUT weirdly and soooooooooooo wonderfully- once my shoulders were mostly in instead of mostly out of their sockets - thanks to that physio teaching me which muscles are supposed to do that job (no other physio even checked which muscles I used, making exercises ineffective) and how to get them working-
I no longer have that ulnar nerve prob
(well unless I've been v lazy about shoulder posture and exercises...)
just a thought for a poss different approach