If you use feeders that can be placed in a shallow, smooth dish I find this limits the substrate any frog/toad ingests - which can limit blockages. Even crickets have a hard time climbing out of a inch high, smooth, glazed dish. Otherwise coco-coco fiber is a great substrate. I'm not sure I agree with the sponge thing, pac-mans like to dig and burrow - it makes them feel safe and comfortable. Unless you have some good hides I wouldn't totally flip over to sponge.

My only other suggestion though is to not over feed him. It's often attractive to over feed a frog or toad to grow him/her larger quicker, but this often leads to blockages and plain old obesity.

And the Vet. suggesting mealworms as a "soft" food option is totally bunk... I find more meal worm shells then crickets remains in the waste then anything. The younger crickets was a good suggestion though. Wax worms might even be a good choice for a while.