Hello,
I fitted a westfalia removable bar and wiring kit to my 4.2 TDI when I first got it and so far as I can tell it is the same as the OEM bar (including Audi markings!).
I specified the actual westfalia wiring kit (rather than a generic vehicle specific one) and coded it with VCDS, again it seems to be identical in function to a factory fitted (but i think the ECU is in a different place for retrofit). If you want the full 13 pin including charging then you need an additional cable also.
It is very neat and un-clips and folds away when not in use so that you wouldn't know it was there.
You can check out the part numbers needed here
http://www.westfalia-automotive.de/
I bought mine from PF Jones in Manchester and collected, they also do delivery and fitting if needed.
I also priced up the equivalent from Audi Manchester and it was over twice the price from the dealers for what I suspect to be identical components!