http://www.mediafire.com/file/qmenmkynjmy/Plex.rbscriptedbehaviour.zip

Let me know how that goes :)

BTW, make sure you uncheck the default Plex behavior in order to use the custom one. Here are Felix's instructions:

"Please note that, when you add your own Behaviour for an app that's 
already supported by a Behaviour that ships with Remote Buddy itself, 
which of the Behaviours will be picked to control the app is undefined.

You'll definately want to make sure that:

- you uncheck the checkbox in front of Remote Buddy's *own* Behaviour 
in Remote Buddy > Prefs > Behaviour (so it's no longer used by Remote 
Buddy).

- you do have only one copy of your Behaviour lying around in ~/ 
Library/Application Support/Remote Buddy/Behaviours"