If it's a static shot, just build a garbage mat pinned to the screen and replace the content with a still frame grab.
If the shot's in motion, you're gonna be rotoscoping.
If you have to do that, you should check out CoreMelt's TrackX - which can automate a lot of that.
If you need actual motion content on the screen that's rolling "live" and synced with the presentation, then you're going to have to get hold of the original screen content and replace it.
Raster incompatibilities like this can't be made to "go away" any other way - they're "baked in" to the signal.
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