The A3 cars get their intercooler air from the lowermost driver's side grille, which has a duct directing all air from that opening (and rocks, and water spray, and the occasional bird) right into the intercooler. You may be able to see the duct and the intercooler at the end of it in the photograph I have attached to this post.
I don't know where the air exits; probably out the back of the front undertray along with the air that passes through the radiator. This probably isn't that efficient but it must work well enough if tasdrouille can block off the air supply and still have low intake temperatures.
Wait; tasdrouille, did you measure your intake air temperature before or after the turbocharger and intercooler?
A3 Volkswagens get their engine air from a hole in the passenger's side fender. This air then passes through a pipe with a few bends, a piece of mesh (the snow screen), a large airbox, the filter, the mass flow sensor and then on to the engine.
Anyway people have been known to drill holes or install a dryer vent grille through their fender liners right behind the intercooler with good results.
I seem to remember that wheel wells containing a spinning tire have low pressure in front and at the back and high pressure at the top and where the tire meets the road. If this is true then placement of the wheel well exit vent would have to be just right. Of course I'll bet the pressures in the wheel well would change completely if it was no longer a sealed area. Anybody have access to a supercomputer to run some calculations?