Ah. My Beastie's previous owner fed him those dried pellets and a few dusted crickets daily for two and a half years before I got him. It's not easy to make the transitions to different foods. I know mealworms aren't the best, but perhaps if you put a few in the feed dish with two or three sleepy, dusted crickets (put them in the fridge for five minutes or so and they'll stop moving around until they warm up again). He might just grab one when he inhales a mealworm and realize they are not awful! And if they're dusted the first time you give them to him, they he won't have to go through another food change when you eventually start dusting them. I know from experience that variety is sooo important -- just keep trying.
Annie
The Worm Lady