It's good that he's still eating.
Chopped ripe bannana is another thing you can try adding to the mix to get some calories into him.
I'd also buy a digital postage scale (you can get good cheap ones from Office Depot, Staples etc.) and get a weight on him. Make the changes to diet and caging as soon as possible. Re-weigh him a week after the changes have been made (don't handle him at all in the interim as this will only further stress him). If he's lost weight when you re-weigh him I'd think about taking him to a vet.
Make sure you make the changes to the cage in addition to the diet. My hot basking site gets a surface temp of around 120 (110 should be sufficient) and the light shines on one of the layered rock formations I described. The rocks retain the heat and it's my chucks' favorite sleeping crack. Since your guy is in poor health having a hiding spot that retains heat after the lights go out may be especially important.
With the lights, you want to make sure that they are on for at least 12 hours so that your chuck doesn't try to slow down for the winter. If you haven't already, you might consider getting an appliance timer to keep the photoperiod regular.
How do his poos look? Have they changed at all since he started to go down hill?
Wild caughts can take a long time to acclimate and the initial stages of decline can be hard to spot. Your guy may have never been eating enough to maintain his wieght and kind of crashed two months ago when his fat supplies were finally exhausted; now he's metabolizing his muscle. Your guy was probably 5+ years old when you got him. Males his age can take up to two years to fully acclimate to captivity under ideal conditions. Definatly don't handle him unless absolutely necessary and make sure that he has several tight rock hides he can squeeze into on both the warm and cool ends. You may also want to cover the front 3/4ths of the tank rather than just the bottom (you can gradually remove the covering when his weight's back up).
When my wc female was acclimating, dandelion flowers probably comprised about 80+% of her diet (her choice not mine), nasturtium leaves were the other big favorite. Keep offering a variety, but if you find something that he really seems to like, try to offer it as regularly as possible and give him as much as he can eat. Once he's back up to a healthier weight you can start offering it less frequently to force him to branch out. Try to offer lots of high calorie foods like grated squashes, yams, and flowers. Some people have also had lots of success witht he frozen veggie mixes. You can also try mealworms and waxworms. Some chucks will take these and it they do, they are a great way to deliver a bunch of calories in a hurry (my male loves them, but my female won't touch them).
Keep trying new things until you hit on something good for him that he likes. This chart hs some good info even though its geared towards bearded dragons
http://www.beautifuldragons.503xtrem...Nutrition.html
-Alice