I recently had a similar situation where I needed to remove a shadow.
I was able to accomplish this with AE 6.5 Standard. (Motion tracking would have helped but that option is with Pro)
If you have access to the “Clone Stamp Tool,” it works much like it does in Photoshop. Create a comp, double click layer, and use the clone stamp to “paint” the shadow away using pixels from the background that matches. Choosing the “constant” option allowed me to keep the shadow out for the entire SOT.
Hope this helps!
Sally
http://www.slewismedia.com