You could try a bit of plain cooked chicken or turkey, mealworms aren't usually a big hit with Syrians though there are some that love them so you could be lucky
Tofu is also worth a try for the protein. What food mix are you feeding him?
I don't have any experience with Syrians but it may be that as he is still settling in he hasn't decided on a safe place for his stash yet, though I'm sure someone may be able to help with that more