Nah, just an idea I had using the same wiring and relay setup I used with efans. I think that's how Dorman wires their aftermarket seat heaters.
I found this schematic for snowmobile heated grips that you could use. Instead of left and right grip, it would be back and seat.
Only thing though is that there is a third wire in each I believe (check schematics). One is for the sensor, which is the other issue is that if it overheats, it won't shut off and.... meltdown or fire.
I was thinking of doing this on my TB which doesn't have heated seats. I got the heaters from junkers and was going to add them to my stock seats.
But did you check too see if the wiring is there under the seat? Maybe all you need is to add the switches to the door modules.