I'm going to suggest something "Boris" first, then give another solution.
You could try BCC Motion Key in the Continuum Complete package. This will try to reconstruct a background image from multiple frames. There's a tutorial on the BorisFX site.
The other way, possibly without tracking, is to create a clean plate then settle down for some good, old-fashioned rotoscoping. Basically create articulated masks to cut out the foreground elements and reveal the clean background plate.
How do you create the plate? Well, if you can't get a good bit of clear footage when shooting, then it's a fair bit of Photoshop work, blending multiple frames and a good amount of cloning.
I've got a training DVD in production that is all about roto work with Mocha. So I'll just say, that depending on your footage, you could be in for a fair amount of post work. :)
Hope that helps,
Ben
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