If you have time to run a test, try this:
Get the shot with the pad turned OFF. Use Mocha to track the pad. Use Rotobrush to isolate the pad surface.
Apply the Mocha track to a nested comp, which is a totally-rebuilt... um, desktop for the pad. You can put anything you want in it.
Apply a blend mode to the isolated pad surface tio give you all those reflections, light glints, etc. to make it look real.
Former Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA
Along the lines of Dave's advice I would add- make the precomp full screen. If you want a real camera move then you'll have to do a 3d track and position your precomp to match the screen in the live shot in 3d space. This way the virtual camera will match the real camera - of course you'll have to adjust the end to have a perfect full frame of the desktop. If you want to do a quick zoom in post, the you need only worry about animating a quick scale up (add motion blur) and position/scale the precomp using corner pin.