My guess would be the actual heating element controller will be a black box talking on some sort of bus that authenticates against the car's controller and maybe even the keyfob as is sometimes the case for mileage. So you might be able to turn it on, but only to like 100% and never get it to be controllable by the dash or voice or whatever.
Rip out the controller and insert your own.
Anything on the ODB communications bus can be picked up by other systems. Maybe they'll claim you've invalidated your warranty.
The ODB port only has to provide emissions diagnostics. Anything else can be isolated.
The OBD port only has to provide emissions diagnostics to you. The machine the dealer plugs into it is a different barrel of bananas.
I mean, rip out the cable that goes into the seat, and attach your own controller.
Depends on the specifics, but it could also just be a pair of wires run from a central body controller. The current's not that high.
I guess you void warranty. After warranty there is no reason why not to do it.