I recently decided I was tired of crappy cassette adpater quality in my Jetta, and bought one of
these - the one that connects at the radio. It uses the factory head unit's CD changer controls to integrate the iPod.
Not content with letting the iPod sit there in the change tray, I took a 5G Universal Dock adapter and used a Dremel to route out the slot where the dock's connector would normally slide in. I made the opening large enough to accommodate the Peripheral unit's 30 pin plug, painted it black, and then superglued it all together.
I then went and bought some black vinyl from Hobby Lobby, and a sheet of 1/4 foam core. I used an exacto to cut out a piece of foam core the exact size of the opening over the change tray area in the Jetta, and cut out a hole for the dock adapter/Peripheral cable to fit in. I then covered that in the Black Vinyl, to better match the black leather interior of my Jetta. Finally, I used industrial strength velcro to attach the assembly to the Jetta, that way it wouldn't be permanent.
The great thing is, the whole setup looks awesome, sounds great, and better yet - works with my iPhone!
Here it is: