Pac audio has an interface designed to be used with a backup camera pn VCI-GM2. I have installed these on both the 2004 (mine) and 2005 touchscreen units. The Pac unit has a video input that overides the factory nav/stereo screen. Since the camera signal is coming through a standard rca cable when you switch it on the your video should play on the screen. There would be no sound with this but you should already have sound capability from your dvd setup ie headphones/fm modulator etc.
Maybe someone with more electronic knowledge could share there opinion whether this will work or not.
Pac-Audio