There may be another way to go.

Don't dump your tuner. Then get the mute line from the phone and through a small electronic thingy inject a resistance value into the tuner sony interface which measures resistance values. then i belive Hijack can take these commands and remap them so this could then switch you to Aux mode.

By small electronic thingy some one on this board could come up with a bread board design in minutes to do this.