Laptop Audio through Stereo?

I'm trying to run audio from a laptop or other external device into my stereo. Does anyone know if its possible to hook up aux. sound input into a stock head unit H/K (non-nav)? I read about the BMWPILA but that sounds like a lot of money for a simple little adaptor, has anyone tried any alternatives? Maybe splicing directly into the wiring for the CD Changer? Are there any aux. inputs in the back of the head unit that i could just plug directly into? I was also thinking about running through the cell phone audio, but that uses a seperate speaker, probably wouldn't sound good, right?

Thankx