Actually, when I play, I start conquering all the minors as soon as I have all the Economic and Research treaties in place with the other civs, and I have chosen my Ethic. (usually evil) Build the spin control center if you can, so that you can be #1 in Military.
When you conquer a minor, you will notice a huge influence shift in your favor - much more than you would expect. Conquer all 8 of them, and you should own over half the map (depending on size). If you have mind control center, that may be all you need to do to win the game - even on suicidal.
So, I trade with them early in the game, conquer them later. I would never have a major declare war on them (I want the planet eventually). Having a nearby minor declaring war on them should work fine.