for the ipod models, there is a connector in the console to hook up the ipod to the shaker. you might see if that connector is available, and try it on the aux port of the shaker. i have not really followed the whole ipod to shaker topic at all, since i dont have an ipod, and my mp3 CDs work just fine for me.
i know ther was also a connector for later model shakers called triptunes. i dont know if anyone has sucessfully mated it to an 05 though. there was some kind of disclaimer about it not working on 05s.