create a custom field for the thumbs and select that in the import options. Edit your player settings and use inline coding to flag true/false for if exists value. If thumb url is there display the custom thumb, if not,,,display a stock image.
example:
http://hugefreeboobs.com/video/828/b...s-fix-my-pussy
http://hugefreeboobs.com/video/2/ang...-with-an-angel