Won't work. Even though you could make youself a converter seperating the audio-input from the CD changer control wires, the radio expects a CD changer to be conneted when you switch to 'CD'. Since there is none, it can't talk to it via the bus and therefor will switch back right away, telling you there is no changer conencted.

anyways if you pull out the radio you will find a sticker at the back telling you the pin layout of the CD-changer conenctor. j.