Change thumbnails for programs

Does any one know how to easily change the thumbnail of processed programs. Mine always comes back showing a thumbnail of my credits. The station told me they might have a process but that was sometime ago and they still have not added it as a feature available for producers

Thanks the new add thumbnail feature when creating episodes is fantastic here is an example of the results http://seattlecommunitymedia.org/node/10922/list-shows before the thumbnails just showed my credits so no way to see a hint to what's inside.