I can't help you with the plugin.
But plex installs quite easily in a regular jail, if you'd like to try that. That's what most of us do. Set up a fresh jail, make sure VIMAGE is on, and after perhaps a "pkg update" and/or "pkg upgrade", you should be able to do a "pkg install plexmediaserver". Then you will have to know your way around Unix a little bit to start it up, etc., but it's not too bad.