Wow, it sounds like he is doing a lot better now, he is growing fast! The hornworms do give
them a lot of hydration. Does he like the BSFL quite a bit to be mixed in with his greens?
If he will take water from a dropper you can continue giving that way for now, which helps
out with hydration when needed.
Keep us posted on him!
You could also try a bath because my beardie was like that and I gave him a bath a day and in a week he was SO much better. Oh and a water dish heated to 95 temp would probably be good.