You can get JP without gaining any Exp. The thing is, at least one person will have to be getting Exp.

Whenever one of your units gains JP from an action, all allies in the battle will get 1/4 of that JP for that Job the one is in.

It's slow but it's the best you've got.


The Calculator also has this movement ability called Move-Get JP. Whenever you move, you'll gain some JP. Not so useful in your situation, considering how many JP you need to even open up the Job. You probably won't want to get JP without Exp by that time.