How? make objects invisible to camera.

I need to make parts of objects invisible to one of the cameras in my scene, but visible to the rest… I have no idea how to do this…
It would be ideal to do this via a color map on a second set of uvs or something; color map a tells the camera not to render that part of the object, an alpha cutoff sort of thing.
Any ideas?
Thanks for taking the time to for read and think on this.