Been thinking about this as well. I found those schematics a while back and was thinking that I would soon pull the radio and hack it using a mini plug with bare wires connecting to the plus and minus on the factory wire harness. Then the trick I think would be to determine which one of the wires in that same harness powers up the CD player so that you can put a switch on it to disable the cd player. Since there is no pause on these units, you would definitely need to disable the power to the CD player to keep from having the signal on your aux input combining with the signal from the cd player.
I have no time on my hands so can't say for sure I will get around to this soon, but why wouldn't it work?
Hoop