If Charlie has been getting nuts since his eyes opened it is very possible that he does have early MBD. If it wasn't for the formula and HHB he would have full blown MBD.
Here is a link to the treatment. Keep in mind this is the treatment for an adult squirrel so you don't want to give a full MBD treatment. I do think he would benefit from additional calcium to supplement the formula and HHB. I'm just guessing here but I would give 50-100mg of calcium (Tums) daily for a week and see if he perks up. Space it out through the day. Don't give it all at one time.
https://thesquirrelboard.com/forums/...-MBD-Treatment
Nuts are a high phosphorus food. The body has a balanced Metabolic ratio of 2 calcium to 1 phosphorus. When high phosphorus foods are fed in abundance the body will pull calcium from the bones to balance out this excess phosphorus. This is what causes MBD. In advanced cases MBD causes hindend paralysis, seizures and death.