There's no way to do that. You cannot hook up an Alpine CD changer directly to a Pioneer radio. Just doesn't work.
You may be able to find a seperate controller that will allow you to control the Changer from a small remote, but there is no way to have the Pioneer deck control that changer.
Edit: Also, this would belong in the CAR AUDIO forum.
And lastly, this is a site about Car PCs. You may want to go to a dedicated CAR AUDIO forum for questions like this.