There are no Aux-in ports on the back of our head units. In looking at the back, it seems to have the connections for a CD changer which could be turned into aux-in. I don't know if our head units can run a CD changer (still have the capability that is).

At the moment you only have a couple of options;

1. Replace the head unit with one that does offer aux-in
2. Install an FM Modulator
3. Use a wireless FM transmitter (not an option for me, poor sound quality)