[Slick]

I still think the best way to undome a planet is to concentrate efforts to capture other-breathing population. Even if you capture one of those suckers, you can breed them and undome all the planets in your empire with their offspring.

You can capture one of the planets, trade, capture a pop transport or a colonizer, use intel, etc.

Don't forget to address their natural trend to unhappiness, though. Troops or one of the happiness facilities is a good way to do that.