I have Rasplex installed and is working fine connecting to the Windows server. However I need the client to go out on the Internet to update, sign into plex, etc.
I am unfortunately behind a proxy server that requires authentication. I have found that in XBMC you can enter all the details for web proxies but I cannot find these in RasPlex.
You will definitely have to SSH in and mount your RO partition as RW... if you feel comfortable doing this, I have a proxy I can use and test the config with you.