when they're new, they can be hiders. have you included anything else in QT, like PVC elbows or plastic plants, to allow him more things to hide in/behind? a couple pieces of large PVC elbow might go a long way to helping him feel secure.
as far as the feeding, i've had fish takes weeks to eat with me even in the room. sometimes the best thing to do is rubber band that nori to a small weight and just leave it in there for a few hours. same with some myses. let them float around for a bit with you out of the room, and see if he picks at all. then come back a few hours later and clean up any uneaten pieces.
i was tank sitting for a friend a few years back, and he had a new bristletooth tang in QT that he was really worried about. it never came out or ate when he was around. long story short, he set up a NEST came to watch it remotely, and the little guy was quite hungry and gregarious when no one was around. but as soon as you opened the basement door *poof* he vanished.
might also be worth pulling some algae rocks (if you have any) from your main tank, to give him something to pick at.
