I don't have a definitive answer. But my rears seats, which did not come heated, do have the wiring that leads up near to the seats... still need the plug-in heating elements placed into the seats (and switches). So, I presume you have the wiring to the seats, but still need the heating elements and switches installed. It would not be difficult to trace the wires to be sure.
Might be difficult adding the heating element into the installed seats. But certainly others have replaced the broken elements in the seats so it can be done.
Check the archives? Let us know what you come up with.

Don