Hi
Have you tried to disable the camera at BIOS level when the system starts ?
Take a look at
http://www.reactivated.net/writing_udev_rules.html you might be able to write an ownership rule to block use of the device.
Unload the camera support at kernel module level.
Just a couple of thoughts.
If you are worried about unsecured use then you could always use the physical approach and put a piece of paper/plastic over the camera when not in use.
Chris