FORGET ALL THAT!
I just ran an experiment on my car... and it was a SUCCESS!!!
I'll provide pics at the end, but for now I'll just explain what I did. I pulled the harness out of the bottom of the TCU, sure enough position 4 was missing a wire. So I took a piece of wire from my tranny resistor project, coiled it up, and put it in through the back of the harness, then put the harness back into the computer. As for ground, I rememebred that the ECU goes into diagnostic mode when you ground pin 2 on the harness... and to do that you put the end of that blue wire in it.
So I coiled up one of the blue wires with the end of my wire. Starting the car saw no change, backing out of the driveway was no different... but damn. I put it in Drive and the POWER light came on and just... it just WENT. Holy crap. I did a test drive around the block and it was just so solid. Having POWER mode on like that is just such a cool feeling.
So I have confirmed that grounding pin A4 on the TCU does in fact grant you unlimited POWER mode whether you have a JDM car or a USDM one. Can't comment on the UK ones, but my thought is this: if they just didn't put in the switch in the USDM TCU, then why would the TCU in the EDM models be different? It's so much easier to just reverse the switch function! If the "POWER" switch on JDM models grounds A4, then why can't the "ON" position for the Economy switch just be an open circuit for pin A4, and the "OFF" position be ground?
Dunno. Anyway, it felt awesome, that was a very cool experiment. I'll have to rig up something more permanent real soon.