Wow i think i just had a revelation.
Crown of Charisma says reveal this card to add 1 die to your diplomacy check
Recharge this card to succeed at your diplomacy check.
It also has the magic trait, and it does not say that it has to be used for a noncombat check.
By simply having this card and recharging it should work!
I have no idea. If it's like Guidance (where you play it later in the check) then it won't work. But I'm totally confused about those rules. So it's possible that it doesn't add the trait.