Wasn't 100% sure on the best way to wire the passenger side, but after no reply, I just thought I would tackle it myself. So obviously the passenger side doesn't have a bulb socket holder, so I had to source and waste money on a corner light just for the socket wiring.
I extended the factory wiring with some 5 amp cables, enough to reach the driver side rear.
I wanted to keep the wiring colour coded but had to make do with what I had at the time. Factory black/white cable being negative, and the green/yellow being earth.
As mentioned way above on the thread, drill through the tail light using a big enough drill bit or a hole saw attachment (a circle outline is engraved, where the bulb sits inside, aswell as ventilation holes around the black bulb housing). Any debris from drilling, use an air line, compressed air or a vacuum to get them out. Feed the wire inside the boot lid reaching the other side.
With the extended wiring reaching the driver side, I used some cable connectors to tap into the factory wiring harness for the driver side rear fog. As shown above, factory black wire is the negative -, and the red/blue being the positive +.
Finished result.