is it a FWD?
I've got some ideas with that.
Certain model A6's use a seperate stub axle and disk on their FWD models. I think, that with a bit of part catalog crunching and some perceveriance, it should be possible to put together a setup using those hubs and some other bits.
The first issue is going to be finding a hub that will physically bolt to the axle beam itself. Then with that inplace you'll need to find a disk that will give you the correct offset etc.
If we're really lucky, it might just be a case of bolting the stubaxle on, and throwing an S4 disk over it and a set of S4 rear calipers and jobs a goodun.