Age-old problem. Not just with that car, but with many cars. How to add aftermarket gear to a heavily-integrated head unit.

Search around and see if you can find someone who makes an aux-in adapter. Try places such as www.peripheral-aamp.com , www.blitzsafe.com , and www.rcainput.com . Even though the port is optical, there's a chance someone might still make one. You're not the only person in the world clamoring for the ability to hook up your own gear to the factory stereo.

Good luck!