Here is something I've done for shows where I have LOTS of extras.... Family Guy, Simpsons, etc.
I just 'created' another show called for example 'Family Guy Extras'.
The I create seasons just like the regular show with the extras from each season.
Using a metadata program like MediaElch to create nfo files (suitable for XBMC/Kodi) since this was my main home theater media player for the longest time... still use it actually.
Anyway in Plex you have to set up your tv show Agent to 'XBMCnfoTVImporter' so it will use the metadata.
You can also select your own artwork and bickety bam you have your own custom shows.
I also do this for other things that have no particular category... For example YouTube series... like the Epic Rap Battles of History for example or the latest one I just did.... Exploring Middle Earth series that a guy is posting. I just download the episodes and do the same that I did with the show extras. Looks nice and polished just like a regular series.
If you don't want to go through the hassle of individual screen grabs for individual episodes Plex will grab a frame from your videos.
Hope this helps someone.
I actually don't prefer the season 00 crap unless its just a few extras.
Something like the Simpsons in its 28th season has way to many extras to cram in one folder.