Library Auto update (Linux)

I want the library to auto update when files are beeing added to the directory i have scraped. However I cant use the built in function as it requires write access (Why the hell would it need that?!)

I'm using rar2fs and all my content is derived from there, thats why I dont have read/write on that folder.

Is it possible to have plex watch another directory (without adding content) and have that update all libraries?

Or is there some way (maybe the best solution) to invoke a library update from a bash-script? Shouldnt be too hard using a combination of tree and diff.