The only thing I know that can do this are artifacts. Being not much of a modder more play tester my advice is slim.

I also tried to do something like this in my mod and had no luck.  In my case, I was attempting to colonize a planet from another gravity well and basically hit a brick wall of minidumps in my attempts.

I believe there are very limitted things you can do that go from one planet to another and I do not think it is possible to "target" more than one planet with an ability.

-dolynick

 Just a thought, but you have probably already looked at the race orbital cannons, yes?  They act from one gravity well to another, also there is the culture spread from the broadcast towers on one planet that extend out to the other planets, in fact over-taking those planets if you build enough of them, then you could technically, though i would have to test it, extend it out to the rest of the system. I have seen chained planets do just that, in fact i lost a game to the vasari, that bombared my whole small collection of worlds with their broadcasters.    

Anyway, you have probably already thought of these things, but just wanted to mention them just in case you hadnt, dont know if it will help with what you are trying to do or not, but worth a try.  

-Teal