Head Unit Key/No Key

I've got a '96 Jetta that I use as my daily driver but I LOVE how my '03 Jetta has a feature that when you turn the car off it turns the radio off and you can take out the key and the stereo will still turn on and off at your dispoal. I was wondering how in the world I can wire it -- i have an idea but I would like a few more opinions -- so that it still turns on and off with the key but ALSO will always turn off with the key but still turn on and off without the key in. I'm sure there's someone on here who will already have come across this question/problem and will know what to do. Thanks.

whenever you think of it just let me know

Anyone else have any idea how I should go about this? Think of it nouseforaname? I have a lot of free time in the next couple of days and would love to get this done and out of the way.