I was finally able to install the plugin by piecing together information from several forums.
I have Plex media server running on a Netgear ReadyNAS ultra 2 plus.
This is what I did to install. (No guarantees it will work for you.

)
1) Download and install EnableRootSSH
2) Download and install WinSCP (an easy to use graphical interface)
3) Download the MCM Plex agent and scanner (other) plugin at
http://download.mediacentermaster.com/MCMPlex_1.01.zip4) Login using username "root" and the admin password for your NAS (if necessary the root user password can be reset to the admin password by following the instructions here:
http://readynas.sphardy.com/2010/09/res ... _4574.html )
5) Place the files from the MCM Plex plug in (other) download in the following places:
5a)Copy the "MediaCenterMaster.bundle" folder into in
BOTH:
/c/.plex/Resources/Plug-ins
and
/c/.plex/Library/Application Support/Plex Media Server/Plug-ins
5b) Copy the entire contents of the scanners/common folder to
BOTH:
/c/.plex/Resources/Plug-ins/Scanners.bundle/Contents/Resources/Common
and
/c/.plex/Library/Application Support/Plex Media Server/Plug-ins/Scanners.bundle/Contents/Resources/Common
5c) Copy the "MCMCustomVideoFiles.pyc" and "MCMCustomVideoFiles.pyc" files (located in scanners/common folder) to
BOTH:
/c/.plex/Resources/Plug-ins/Scanners.bundle/Contents/Resources/Movies
and
/c/.plex/Library/Application Support/Plex Media Server/Plug-ins/Scanners.bundle/Contents/Resources/Movies
5d) Copy the entire contents of the scanners/series folder to
BOTH:
/c/.plex/Resources/Plug-ins/Scanners.bundle/Contents/Resources/Series
and
/c/.plex/Library/Application Support/Plex Media Server/Plug-ins/Scanners.bundle/Contents/Resources/Series
6) Close WinSCP
7) Restart NAS.
Hopefully this will be able to help others having the same problem.