There are two ways you could do it.
1: You can use the CD changer input. Sony might make an adapter. Someone else may have already done it as I havn't.
2: Get a FM modulator. It connects between your head unit and antenna and allows you to input audio through your FM radio. Many people will tell you not to go this route because it degrades the sound sometimes. I personally went this route and it sounds great to me, since it doesn't transmit the signal through the air it is better quality than a normal FM station (IMHO).