You could try copying stuff from the PPP/whatchamacallit intel op, (where the planet
dosen't join the attacking empire), and see if that ability can be used in a random event.
It would be kinda funny if you could put that ability into a ship/component
. The planet that built the ship immediately breaks away from your empire, and any other planets that the ship visits will also break away from their owners (friend or foe)
It would be like a MAD situation, except that nobody actually dies!