Some snakes wont eat with an audience. Dont mess with him at all for a week, then put his thawed dinner in his enclosure with him overnight. If you can place it a few inches away from his head without bothering him at all, more the better. If you cant, just put it on the ground and close his container. I like to leave food at midnight. If they're going to eat it, they'll find it while hunting during the night. If he wont accept your first offering, try leaving one for him every few days.
I've got 2 poor feeders. Through trial and error I've discovered things that temp them. 1 insists on a rat fuzzy, he likes it warm and he likes it to "run" from him on the tongs. I get his attention with it in the tongs and then start guiding him along with it. He normally grabs it pretty quick. The other likes mouse fuzzies scented with quail blood and a chunk of liver on its face. Really. I have quail here anyhow so its no biggie, but you may find some luck with chicken liver or egg yolk. I also have a rat snake that didnt want to do thawed so I took scissors and cut the skull of the fuzzy open to expose the brain juices. Worked great.
Do your best to leave him be between feeds, dont take him out at all, no matter how much you think it doesnt stress him.
I container feed my snakes, but I'd leave a really fussy eater in his enclosure if I necessary. Each snake wants different things, try tweaking your enclosure a bit, more or less temperature, more or less humidity, different substrate, hides, etc. If the enclosure is too big, try something smaller or give him a very small hide box so he can feel secure. They're largely very good eaters, though a few hold out until we offer them what they consider to be appropriate food or housing. He sounds like he's eating enough to at least sustain himself while you figure out what makes him tick.