Well folks, I finally worked out how to get a USA model ECU working on a Euro/Aussie 6th-gen VFR. Took me a while though as I had to map all the pins on each ECU until I found the culprit, but it's actually a very simple difference. Note that the following is only guaranteed on a 2006+ model bike.
The USA ECU has two power inputs into it. They are both the Black/White wire 12 volt input from the engine stop relay, and one goes to the black connector while the other goes to the grey connector.
The Aussie/Euro ECU only has one power input. It is also the Black/white wire but only goes to the black connector.
In order to easily drop in a USA model ECU into a Euro Aussie bike, you will need to add a pin and wire to pin #16 on the grey connector, and then splice that wire into the black/white wire feed from the black connector. Once this is done, the bike will fire right up.
Now, there's a small "gotcha" here. And that is the fact that you need to find a connector pin from somewhere! Unless you happen to have a bunch of wiring harnesses lying around (*cough* Kaldek *cough*), your only option will be to remove one of the pins used for the HISS circuit and move that pin and wire across to pin #16 on the white connector. I haven't traced exactly which ones of these is the best source, but once I do I will add that to this post, along with some pics. :-)
If you plan on only making this a temporary modification, I would put a switch on the spliced wire feed into Pin #16 so you can safely cut that circuit before you connect an Aussie/Euro ECU back into the wiring harness. If you don't do this, I guess there is a chance that you could create an internal short circuit inside the ECU (which would be bad).