Please, please help me feed this ridiculously picky creature.

[Mr. Misha]

With these current changes, his temps are now 75-77 on the cool side and 85-89 on the hot. Humidity is up to 55-60 with occasional misting.

You're heading in the right direction.

Don't worry about UVB lights or lights at all for that matter. Ball Pythons don't need UVB lights because even though limited studies have been done (see links below), they are not even sure whether BPs can metabolize D3 vitamin so don't waste your money.

https://veterinaryrecord.bmj.com/content/173/14/345
https://www.researchgate.net/post/Is...captive_snakes

Your cool side is definitely still a bit low.

If you decide to use your 10 gallon, that's probably is going to be your best bet. With the current CHE acting as primary heat source, it should be more manageable for you to keep temps around 80-82 on the cool side and around 88-90 on the hot side. With all the stuff you already have in the 40 gallon, you should also be able to make a nice environment for him.

As someone already mentioned, constant feeding does stress your BP out so give him a break for about a week.