If you want something that is rather... instantaneous, then you can mod the domination ability, make it work for capitals, frigates, planetmodules and planets.
It converts!! i havent looked at the buff for this for awhile, but it may be possible to delay the change over by a time period? Say the delay? But you will have to look if you want the take over to take some more time rather than instantly.
But it works very very well.
And it doesnt kill anything.

-Teal
Ooops!! didnt see Terraziel's answer, but that is what "ChangePlayerIndexToFirstSpawner" is. 