Got it all figured out. I tried a 100K pot and the relay pretty much triggered at 1.2V on hi limit setting. So with the RD on, I used to pot to dial back the 3v idle voltage until it got just under 1.2V. This way the relay only triggers on an alert.
Looking at my picture above, I tapped into the yellow wire for the alert. This sits at 3v during normal operation and spikes to 8v on an alert to trigger the transistor to ground the alert LED. I was able to do this down the line with a t-tap so I did not have to solder on the small control board. I wanted to remove the seat but it was really cumbersome and my back wasnt liking it, so I just removed the rear bolts and unlatched the front so I could slide the whole assembly forward. The seat bolts were large (T-50?) and had blue locktite so they were kind of a bear to break lose. I did add more blue thread locker when replacing. The negative battery terminal was removed before disconnecting the main seat harness as it has SRS components in it, but in hindsight, since I was not removing the seat I could have left that connector intact and just removed the negative battery terminal.
To remove the seat cover, I had to remove the front seat panel which was just held in with clips, and the outboard seat panel, held in place by T-20 bolts front and rear. There is a connector for the seat controls, and after that is gone, the seat cover is held in place by a metal bar also with two T-20 bolts. This is the only part that would be very hard to do with the seat not moved forward off its mounting point. Once the bar is gone the cover is held by j clips on the side and front. I was able to peel back the cover maybe 1/3 to 1/2 way. The foam in the side bolster was torn and dry rotted, so I added some foam I had laying around as it was hard to not tear it more when replacing the cover. It seems the adjustable bolsters are not kind to the foam. I am not so sure the cover is supposed to be separated from the foam, as there are clips that tear away from the foam when doing this. It is also held down in channels with velcro. I used my fingers to tear out a cavity for the motor a little forward of the existing haptic motor and stuffed it in there.
I ran the leads down the front of the seat and under the carpet to the edge of the car then up under the dash. I've never seen car carpet with so much padding. I am guessing this is cut down on noise. It also explains why it is so tough to get good exhaust sound out of these cars I think. Moving the seat back off its mounting points was also required to hide the wire under the carpet. I tried several different fishing techniques with the seat bolted in and no dice. The insulation further complicated things.
It was very tricky to get the seat cover back on properly. Just stretching it over the bolster pulls foam down with it and you end up with a weird looking seat with hard spots. I had to keep making sure to keep the bolster tucked in as I pulled the cover over. After that I replaced the seat trim, bolted the seat back down, cleaned up the motor wires a bit, and reinstalled the rocker panel trim where the carpet meets the car body. Wiring everything up wasnt bad, I did it all under the kick panel above the pedals. Right now the relay and pot are just a mess of wires insulated with electrical tape, but I will have a small enclosure for the set up installed soon. I pulled off of the power wire for the RD, so it is fused with a 5 amp fuse which I think will be plenty sufficient, but I considered ordering another tap to take power from another branch. The relay itself only pulls a few mA and the motor cant pull very much either. This is pulled off of the wireless charger fuse location, as this is one of the few circuits with switched power. It wouldnt kill me if it blew since I dont really use that cubby hole for charging.
I would also like to use resistors instead of an adjustable pot but I am not good enough with electrical theory to figure that one out, so I will likely leave the pot, and secure it either to my enclosure or the kick panel. This would also allow for a disconnect for the motor since turning the pot all the way down will stop the relay from being triggered no matter what. The seat harness is right at the front under the seat so it would be cool to tap into the existing haptic motor with a diode to prevent confusing the seat module, but I am too scared to do that without a scan tool that can clear those DTCs.
If anyone wants part numbers or has more questions let me know. I am not sure how different this would be on the non Recaro seats but would guess without the adjustable seat bolsters it may be easier.