Maybe he just needs a bit more time then. Two of my current fish took longer than others to really get comfortable in my tank. My potters angel didn't eat at all in QT for about a month, and for the first couple of weeks in the display. My moyer's wrasse took a 7-week sand strike, and came out looking ok. Took about another week to fully settle in and join the routine.
Both now eat anything and everything and are out with the group constantly.
I'd say, maybe smaller, more frequent feedings... making sure to squirt a bit near his hiding spot so he reach it without having to come out too far. Also could try clam on the halfshell, or pieces or shrimp, scallop, etc with a pair of feeding tongs.
