Sounds like your vet doesn't know much about frogs. First of all, answer the questions in the Trouble in the Enclosure sticky. I imagine your temperature and humidity are probably a little off. That can cause them to act funny and get sick.

What does the vet have you syringe-feeding him? It's good that you're getting food into him, but stress can be a huge problem for frogs, and force-feeding is very stressful on them. Hopefully you can get him eating normally soon.

Coco-fiber is actually the recommended bedding for pacman frogs. Unless you feed in a separate container (which I don't recommend for skittish or stressed out frogs, as it just stresses them more) moss is a bad substrate. It can and will be accidentally eaten when the frog strikes, and this can cause impaction. No need to rush and change it as long as you're syringe feeding, but coco-fiber works best.
Moist paper towels (soaked in treated water) are fine, but just out of curiosity what is he doing that makes you think he dislikes coco fiber or moss? They enjoy burrowing, and a happy, healthy pacman frog will often sit in the same spot without moving for days. Hopping around for no reason is actually probably a sign of stress.