He's definitely in better shape than some of the dragons I've had - that's always a good start.
If you haven't already, a shallow, warm
bath for 20 minutes would certainly help. Keep a very close eye to make sure he doesn't nod off - you don't want him breathing in water.
If you can get hold of it (your vet certainly can), Oxbow small herbivore mix is a miracle-worker. It's full of nutrients, low in protein, it mixes well with calcium and goes through a wide bore baby medicine syringe with ease - blib it on the top lip scale, and run the tip of the syringe under the lip to trigger licking, then continue supplying to the top lip. A couple of 3-to-5ml feeds a day will soon have him in good shape. Don't worry if he doesn't eat all of the portion - little and often works well, especially combined with plenty of time under the basking lamp.