XXXXing dickwads made me go through my FSM for my truck. I'm going to assume all the WJ stuff is the exact same setup as my truck (which I'd be surprised if it wasn't).
There's the CTM (Central Timer Module) located under the dash that controls a lot of the interior accessories, so you were right there. There is a positive feed to the control module sent through a fuse and relay from the battery (not sure what pin on the WJ).
The module receives input from the temp sensors, and sends the battery power to the heating element depending on which switch is pressed and at what temperature the elements are currently at.
So it looks like all you need is the CTM. If you don't have that, then I wouldn't even bother hooking it up.
You could also probably manual wire in the ZJ stuff.
Why do you need the heated seat portion anyway? I say eff it.