Let the enemy either retake it OR le tthe rioting eventually lead to a full fledged rebellion (I believe this is possible) and when it happens send a ship with a plague deployment system.
Wait a few turns nice empty planet for you.
Then again for the most part with me if I know the enemy is likely to riot I just send in plague warheads right away wait a few turns and go in with transports with a handful of troops and a boatload of population
