Seatbelt sensor should be similar to what Ichi posted, just find the correct plug and put a resistor in it.
I don't think you'd be able to swap the stock heat pad into an aftermarket seat, unless the seat happened to be shaped similarly to the stock one and left enough of a gap to fit it in. The wire fishing alone would be a nightmare. I don't want to say it's impossible but it definitely seems like something you'd have to get a custom job for.
Lol this reminds me of when I first posted on here asking how much weight I'd save removing the heat pad. Good times...
