easiest solution without taking your headunit apart: PAC makes modules that add RCAs to stock headunit, and others that allow you to create an auxiliary input.
PAC AMP-RCA USED WITH ADD CABLE ShipSound.com
Pac-Audio.com Product Details | iPod Integration for your car and More by Pac-Audio - Connecting you to the future

if you go this route, be sure you get the model you need. i just did a quick search so you get the gist of things.