How do you put a single DIN headunit in a car with DOUBLE DI

How do you put a single DIN headunit in a car with DOUBLE DIN stock?
I've got a 2001 Audi A4 with a pretty weak stock stereo system. I plan on adding an aftermarket head unit with an amp and sub. My question is where can I find a mounting kit to fit my dash perfectly?

There are a couple ways. Many car audio shops will sell you a blanking plate to fill the bottom half of a double DIN hole. also, you may be able to purchase a DIN pocket which is just a pocket that fits in the hole, which can hold cd's or another odds and ends. Some of them have doors and some do not. I could check the audiworld.com forums to see what others have done.