Ok, Its finally done. Valet mode lives.
My 99 HSV R8 didnt have a wire connected to the right pin. In fact nothing was connected at that point, just a hole in the connector. The PCM had the pin to accept the wire, so I did some investigations.
I thought I might know where I could find some wire with the right connector socket to fit the pcm. I ended up using a piece of wire from an old computer case. You can use one of the wires that connects to the mainboard for speakers, power on led, reset switch etc. The end that connects to the mainboard can be separated from the plastic "jumper" with a pin. You end up with a piece of wire terminated in a small metal socket.
Ok next step was to get the right pcm socket. The custom OS tutorial has the details for this. The socket is also numbered so its not too hard. I had to poke the rubber seal through with a fine drill bit then pushed the wire through. It has like an arrow head tab on it so it goes in one way and doesnt come back out. This helps when you push the pcm socket back onto the pcm so the connectors slip over all the pins and dont come back out.
Once done I just needed to extend the length of the wire to a toggle switch. Actually Id got to this point a few weeks ago. However drilled my first hole slightly too high up, so I left it lying lose. (Bad idea as the car cut out on a couple of occasions during some spirited cornering! At least I knew it worked)
Anyway got it all wired in properly today. Just a simple 2 pole toggle with open and closed (earthed). Works well. Pretty well hidden if you mount it on the header tank bracket. But some may like to put it somewhere more stealth. 20mph and 2000 rpm max on valet now, works very well.
Just wanted to let everyone know, just in case they had the issue with no wire available to tap into. Just swipe one from an old PC