@ Neo and Lee:
Have spoken again to Chris and he thinks that the "relay interface" he's got (towing thingy box I mentioned earlier) doesn't need VCDS and he pointed out that its wires are capable of handling 3 or 12 volts through the same wire. He's got experience of using this relay interface box.
His next move is to email you, Neo, with the info you've discussed. (Yes, he has your email - My bad).
So far, so good and I'll keep up my job of coordinating and chasing so it all happens. Lee, we know you're willing and able and waiting in the wings if we need your input, mate.
I know the controller does not require VCDS itself, but it may be necessary to set it so that both reverse lights work. Not sure, I'll wait 'til I've seen the datasheet and had a good look-over and seen the functionality.
Please bear in mind that it may be a little while before we get these - We've got to look at what sort of data we have to work with, I've got to design and lay out the PCBs, then we will get some one- or two-off prototypes made and assembled (which will probably be fairly expensive, maybe £50/side as a rough guess as there'll be machining work to be done etc). After that they need to be tested off the car, then on the car, and make sure all the functionality works as intended. After that we can got to a batch PCB house in China and get a whole bunch made for everyone, that will be a much more reasonable cost but the downside is that the batch processing will take some time (IIRC used to be 14-30 days, but may be less now).
After they come back, they'll have to be assembled, and tested, and then (being an auto engineer) I think I'd insist on a conformal coat to protect them, btu that shouldn't take too long.
The end goal will be for some inner tail LEDs that will be reasonably priced, built to near-automotive standard, and capable of a variety of functionality - "normal" operation (on with sidelights/dipped lights), brake functionality (if desired), and fog-lamp functionality (if desired) with the two inner filament lamps being used for reversing lights. No point messing about with half-assed fixes and electronics that will break over time.