I am a car electrical installs hobbyist. This is what you need to do. Find anybody that knows their way around 12 volt systems, and get them to do something like this:
http://www.msprotege.com/forum/showthread.php?t=93147
If you don't know anybody, PM me. I don't mean that extreme an install, but from what I understand, you can use a jack in the back of the factory headunit intended for an optional CD changer, as an auxillary input. If you do a good clean install, it'll look even cleaner than an actual AUX.