Mess with the Mantles (this may not be possible... but if it is...)
Faerie-tales have selkies & swanmays & the like: fey shapeshifters, who can shed a skin and become essentially-mortal; steal the skin and you have captured them.
So far as I can see, the Mantles of power are (non-physical?) "skins" that empower the leaders of the Courts.
We already know that some Mantles can be taken off and put back on at will... a being who "owns" the Mantle but is not "wearing" the Mantle is NOT acting in (nor obligated by) the empowered role of the Mantle-Bearer (I am wondering if that might just be the "fix" for Dresden's little Winter-Knight problem -- take off the Mantle, get his mind in order without one of the Queens getting into his head, and don it again ONLY when fulfilling his deal with Mab...