After doing a fair amount of making up diagrams and looking for hardware it seem to be like most people are saying, just get aftermarket seat heaters. It turns out that the seats I picked up did not have heaters anyways, which made my decision for me. It would be possible to use the seat heaters, but you would need: Relay, DC converter, heat sink, voltage regulator or programmable current limiter, and a switch. There is a more shade tree way of putting some in line voltage limiters which would heat up themselves, but is a little suspect. I am not sure if it would be possible to contact one of the seat companies, like Rostra, and ask for a new complete wiring loom. The hardware for the seats was going to be about $45-65 per seat, I was able to get aftermarket seat heaters for both front seats for $50 total shipped. Still pretty cheap considering its a much more comfortable seat, leather, has power recline and lumbar, adjustable head rest, and now heaters. Plus, that map pocket in the back of the seat is actually pretty handy since the XJs do not have much for cubby storage.
Sorry if this wasnt the solution we were hoping for, but at least its not overly expensive either.