I've been planning on doing heated seats since last winter. From what I had planed I was/ am goin to mount the switch on the plastic piece of the seat down kinda bye the hight adjustment lever. I was looking at aftermarket heaters though.....not too sure about the WRX seats.
Well there's a few blanks on the driver side near the headlight adjustment and IC spray that would work well for the drivers seat switch... I'd just need to find a switch that would fit and match reasonably well. I'm not sure what I'd do for the passenger seat though.