mud flaps, roof racks and now tow bars? Has the world gone mad? 
they bought the wrong car.
Surely that just emphasises even more how much of a do everything sort of car the GTI is?
Tow mounted bike racks are the way to go. I've got a Thule platform 3 bike one. The bikes are away from the car, it's got it's own lights and number plate and it tilts out of the way to allow the tail gate to open.
As for tow bars, I would recommend the Westfalia detachable ones. I've got one on my Passat and you'd never know it was there when the detachable neck was not fitted. I got it from P F Jones in Manchester. I had a look on their site and whilst the list one for the Mk7, it doesn't mention the GTI. It would be worth while giving them a call.
With regards to wiring, I have the full factory 13 pin kit as I tow a caravan. You would only need a 7 pin lighting socket with a bypass relay. If you go for factory kit, it will talk to the car too much. When your lighting board is connected, the car will think it is towing and alter the ABS and stability control settings accordingly.
