I know you don't want an adapter, but the easiest way to do what you're trying is to get the Blitzsafe adapter. They're around $70, and plug into the CD-Changer port. I added one to my Golf, and now I never use the CD player. The nice thing about the Blitzsafe, is I'm able to keep my in-dash CD player and have the ipod. I can play tapes, CDs, or MP3s.
As far as making something work, I bet you could create an aux input via the CD control, but I'd have no idea how to do it. Good luck with that.