From comments in the “eye-podding” post (below), here’s two more websites that deal with hooking up your music machine to your driving machine.
Seth has instructions on how he installed and Aux input into the dash of his Saab. It appears to work off a toggle switch and function OK.
It should be noted that you take stuff like this on at your own risk. It’s your car and you’re an adult making adult decisions. I haven’t tried this stuff and its appearance here ain’t an endorsement – I’m just passing on the fact that these sites are available.