This was a life saver. Other than the secret latch release, taking everything apart and getting the new seats in turned out to be pretty intuitive. You do need a T47 socket which you might not have and a big breaker bar (or preferably a powerful impact wrench) for 2 of the bolts as they were in much tighter than the rest. The outline of the procedure is...
1. Take off the bottom seat cushions.
2. Take out center console
3. Unattach wiring harnesses. Under the center console is a "hub" where a single wiring harness comes in from the car and then each of the heaters (bottom left, bottom right, back left, back right) have their own plug.
4. Unattach the HV wiring holders (you'll see what I mean, it sounds worse than it is)
5. Unscrew the bolts holding the metal frame in. There are, I think 6 11mm and 2 T47s. The 11mm come out with just a regular 3/8 impact wrench but the T47s need more encouragement to come out. Thankfully I have a 1/2 impact.
6. Unlatch the tops of the seat backs using the secret latch (like if you were lowering your non-exec seats) which will then allow you to take the seat back out.
7. Take the metal cage, which is already unbolted, out.
8. Put the new (used, in my case) metal cage in
9. Put the left side back piece in by first sliding the post thing that sticks out of the side of the seat into the hole in the metal cage that sticks up. Next bolt the bracket on the other side of the seat back to the car (This is slightly tricky as you have to fold the seat different ways to get the bolts in. The exec seats don't use these bolt holes so I had to go buy 4 bolts from HD. They're the same thread as all of the 11mm bolts which is m10x1.5)
10. Bolt the center seat belt bracket to the metal frame. Use a new bolt for this.
11. Put the right side seat back in by first lining up the hole on the inside so that the post thing from the left seat back goes in the hole and then bolt the bracket to the car.
12. Put the seat bottom in place
13. Put the bolsters in place
I have no idea if non-exec cars have an unused wiring harness for heating, I would assume they don't. The rear seat heating, as far as I can tell, is controlled through the app only. If there's a way to control the rear seat heating on the MCU then I don't know it. You could probably hack together a heating control that mounts inside the center console if you really wanted to which would kill 2 birds with one stone (don't need to worry about modifying the car's firmware to control the heating with software, and provide the control to the people in the back seat so you're not fumbling with your app while driving or giving app access to rear seat passengers)