Nope, but the idea is cool.
Personally, I'd rule that immunity to mind-affecting would grant immunity to diplomacy, as well as the other cha skills. I see them as EX mind-affecting abilities. But as long as the immune person is willing to listen, he is effectively lowering his immunity, and I'd allow a maximum shift of one category (unfriendly to indifferent), or able to be bluffed.
