I have been playing a bit with this but I think it may require Alan to implement some changes at the software level.
Ever used a doggy DV Camcorder?
Specifically one with a dying or misbehaving sensor.
This shows up as either a dead (black pixel) or a very bright pixel at the same place in every frame. This more often shows up when you have to "push" the brightness because the clip was filmed in poor light.
What I have been attempting to do is to fix this using "get colour from bg" .
What I have done is to create a very small image (1 pixel surounded by 8 semi transparent pixels).
Far from perfect but it does tone down the effect of a black pixel on a white subject and vice versa.
The beauty of all of this is that tracking is not required.
Ideally if we could select to use the colour of a neighbouring pixel rather than the pixel directly below he image that we are using to mask the dead pixel this should be very effective to fix the problem described above.
Some what limited application but interesting.
If my words are not clear i can throw together a few stills that may help.
This is similar to a process called cloning. In phostoshop, you clone parts of stil images to replace other parts.
In After Effects, and other compositing software you can do the same.
In those instances, you would usually move the cloned area around so that it moves with the video, but in your situation, the spot always stays the same. I like your idea. If you can post more info on it, it may help other people.