Tried it and didn't work.
The frustrating part is that when I started organizing and renaming trying everything Google suggested, I had Plex show the bonus tracks in the season directory. But then I tried putting them all in a /Featurette folder and in all the renaming attempts I couldn't get it back to working like I got one season working.
So I know if I name it right like s00Exx or -featurette or something I can have them in seperate seasons. They're not labeled right by Plex but its better than not showing up at all.
I also got it somewhat working by putting them in /Doctor Who (1963)/Specials. But each has to be renamed to match themoviedb.org episode number.