You can try our RE:Fill product ($99.95), which is a plugin set designed to solve this kind of problem. You simply paint a matte once for where the spot is, and then provide that to RE:Fill to fill in the hole based on surrounding pixel colors at each frame. Try our demo, available here:
http://www.revisionfx.com/rfil.htm . Make sure to look for the short HTML manual which is put on your disk with the plugins upon installation.
Pete
RE:Vision Effects, Inc.
http://www.revisionfx.com