How to Disable An LCD Projector Display

We are using an LCD projector in a computer classroom where students have their own workstations. The instruction philosphy is hands-on by the students with minimal instructor intervention. The idea in using the projector is to display an occasionalquick demonstration and then have the students repeat the exercise on their own classroom PC’s.
Question: Is there a way in Windows ME, 98SE and XP for the instructor to easily toggle the LCD projector image on and off (or to a blue or blank DOS screen) from her workstation so that the projector display does not continue to distract students who should be paying attention to their own monitors?
Thanks for your help.