I've resurrected this thread as I really need to get the nipper in the front seat at the same time as carrying something in the rear with the rear seats folded. I would use my S3 in the same role instead of the A4, but the seats are too bucketed to take a full size kiddy seat (rock-a-tot size was fine).
From the answers above it sounds like it is possible, but the dealers will either take me to the cleaners on cost or simply not do it - I'd prefer a professional fitment from the dealer as I don't want the fireworks going off inside the car.
The insurance aspect worries me though, it seems odd that they'd disallow it even if it had been fitted by Audi themselves?
Audi must have saved all of £2 by not including it as standard...
Any more feedback would be most welcome.