Installing AUX input on stock radio

So I just became the proud new owner of a 2006 Buick Lacrosse CX.
Trouble is, I've become very accustomed to playing my music off my iPhone when I'm driving, and my old car had an aftermarket radio with an aux input right on the front plate for doing just that. I really want to keep the stock radio and looks of the Lacrosse, but I'm going to have trouble stomaching the huge step backward to using CD's again (blegh).
Does anyone know of a good DIY way to install an AUX input into the stock radio?

I helped a buddy of mine put one of these in his Hyundai a few years back. http://www.amazon.com/iSimple-IS31-Antenna-Modulator-Aftermarket/dp/B002U5XPBE
He's been pretty happy with it so far.
Sonic Electronix or Crutchfield would have more customized kits that wouldn't use the antenna and might give you a little better audio quality but those would be a little more expensive.

I am going through the same thing. Not sure what I,m going to do yet. I have looked for factory stereos for 2006 buick lacross but the only one that has the aux plug in is 6 cd changer one. Don't know if it would fit. Good luck.