If they won't accept mealworms keep them off food for a couple days and offer them again. I've never had a leopard that didn't eventually eat mealworms. The youngsters seem to switch more easily than older animals.
It might take a little while, but they'll switch over.
Also, you can try putting the mealies over on the hot side of the tank to get them moving, mealworms really seem to hate heat, causing them to they wiggle around like crazy.
Good luck.