If you think he may be suffering from long-term dehydration you can do a brief soak of (treated) water mixed with room-temp unflavored pedialyte (I think it's something like 50/50) which I've found can bring a sluggish baby back to life.

I would also suggest feeding a small f/t pinky mouse once you think he can handle it. It seems like a number of supplements contain beta carotene as opposed to directly containing fat-soluble vitamin A, so it isn't super available to pacman frogs. I personally supplement with Repashy Vitamin A powder along with other supplements, but you have to be sure to follow the dosing instructions for that one. If you can get him tong trained, you can probably also feed him zoomed pacman food mixed with your supplement powder, which is what I use to deliver supplements because it can't rub off like with worms and crickets.

The above is how I got one of my calcium-deficient babies back to health, but I admit it's a matter of persistence and luck as well.