Only stupid question mate is the one that never got asked.
Well the answer is Yes.......and No.
Its perfectly possible that you could have a solid disc that is drilled and or grooved on any car, it may be possible to find somebody who would sell you a drilled set of solid drilled or grooved rear 286mm discs for the MK5. The Brand of Zimmerman at GSF car parts would be a good starting point.
You're also right about having to change the calipers disc and carriers if you were planning on going vented on the rear.
Theres a load of threads about the virtues of bigger rear brakes, make a brew find a comfy chair and search for S3 rears!