Simple iPhone cable

OK, I was surprised that I was not able to locate a post that already addresses this question, so I am posting it here.

I have a 2006 530xi sedan with Sirius and the changer in the glove box, but without nav.

I want to connect my iPhone for music purposes but don't really care about steering wheel controls or displaying information on the idrive screen. I just want a good, direct signal to the amp.

So, here is my solution. I would like to remove the changer and create a custom wiring harness that just taps into the audio inputs used by the changer. Then run the cable out of the glove box for connection to the dock port on the iPhone. Seems simple enough. Why is there not already a commercially available cable to do just that. Or is there one? Or is there something that I am missing that would preclude this seemingly simple solution.

I took a similar approach with an old Acura Legend and have some decent experience doing this sort of thing.

I can't be the only one who wants only audio and doesn't care about the idrive display or steering wheel controls.

Any input would be greatly appreciated.