Oh.
Well, seeing as the courtesy lights are ground actuated and the parking lights are 12v actuated, wouldn't my original diagram work?
Courtesy parking lights (Ground and 12v actuated)
Live:
EveryCircuit - Porsche Light Diagram
Courtesy lights off:
Courtesy lights on:
Simplistic:
I know very little about electronics and there's probably a very simple explanation to why that doesn't work

I just don't want to over complicate something that could be quite simple.
Sorry, just don't want to overlook the most simplest options by accident.