assuming cameras can be turned on and off at will, add an output to the relevant phys brush something like OnAwakened -> [cameraname] -> switch on (or whatever).
if cameras can only switch from one scene to another try making one scene a totally black room (so it looks like it's off), and then having the camera switch from that to the scene you want to look at
i take this is some kind of motion-sensor thing you want..?