Is this somehow different from "Civilization Manager " (F6) -> "Governors" -> "Planetary Governors"?
I think I know what you are talking about, but I can't seem to ever find it when I go look for it. Mind you, I don't think it would work quite right for me, because I care about "readability" of my planets, which requires that I place the planet improvements in such a manner that I can quickly determine what a given world has at a glance. I don't think I can tell an AI governor how to place planet improvement in a certain arrangement that works for me.
If I end up finding it, I'll go play with it to make sure.
Edit: What do you know. When I say I can't find it, I end up finding it within the 5 minutes. I'll go experiment now.