Hi,
currently I am thinking about a library without any thumbnails esp. for sport recordings. Unfortunately Plex always generates thumbnails. Therefore I have the following idea: Why not adding an agent which copies a static image to each movie found without adding it manually?
First commit can be found here: https://github.com/daeks/StaticMedia-Agent.bundle
Attached dummy.png will be placed automatically as poster. It can be overwritten by option (full file path of image)