Automatically the cop in me asks "What are they so worried about anyone seeing"? Most folks I know, if anyone got in and watched them through their webcam, the cyber voyeur would go away out of sheer boredom.
Maybe a little paranoia will really make them pay attention to what they're doing, so you should be able to use this as an advantage.
"I don't need to watch you on your webcam...I'm watching what you type"
