How low is the car? If he's running spacers agressive enough, is he going to run into rubbing if he doesn't stretch tires?
Also a picture might help make a guestimate, but measuring in mm will honestly give you the best estimate. Usually when I'm trying to figure something like this out on my cars I will look around on forums and see what wheel specs people run and how it fits on their car to get an idea what offset is flush. From what I've seen on VWs/Audis, getting offset near +20 seems to be a pretty good start.
I simply measured wheel to fender on my 337 and I'm running 10mm up front and 15mm on the rear... impossible without stretch in my case.
Front
http://i24.photobucket.com/albums/c8/eightsixgts/random005.jpg
Rear
http://i24.photobucket.com/albums/c8/eightsixgts/random003.jpg
Legit
http://i24.photobucket.com/albums/c8/eightsixgts/random004.jpg