I agree that a vet would be a wise. Now the feasibility of that may depend on your circumstances.
But I think giving it a BIT more heat, a good humid hide would be a good step. My leo's humid hide is made out of one of the notecard holders. I split the lid from the bottom and cut a line in the lid so it could fit into the bottom. Then I cut a 2"X2" hole in the bottom. I line it with paper towels that I keep damp and change about once a week. Other great containers are those gladwear tupperware things. Also maybe start giving him a few waxworms and slowly seeing if he can take on weight.
The problem with malnutrition in any organism is that if you give them even the recommended amount of vitamins and nutrients, that can cause shock and chemical instability in the animal. They need to be gradually given precise amounts to get them back to stellar condition. That's something you can only trust to an experienced herp vet. I do think it's good of you to do what you can for the little guy.