I'm glad to hear he's doing so well.
First of all, don't mess with the little one's eating very much right now. If all he wants is crickets then give him crickets. Someone suggested letting them go hungry for a WEEK (OMG he obviously didn't see the picture), but that you obviously don't want to do with the skinny one. What Ryan suggests is gross but it does sometimes work (the head cutting, etc). You could try that with both leos. Just don't worry about switching over the little one right now if he's not inclined to. I can't believe they won't eat a waxworm tho. Once they taste one they won't stop I bet. Try Ryan's method on a waxworm too.
Oh also sometimes a newly molted mealworm (it looks white, stays white for about 15 mins) looks good to them. If you see one white, offer it to them.