Maybe a list of media folders would work better (A simple text file in one place could do this)
IE, you tell it where the media is, and if it finds that file, it only shows those folders (otherwise it just shows everything)
Very simple, and VERY low overhead memory-wise.
Since most people only have a few specific folders for this kind of stuff, it wouldn’t be a hassle to do this.
Note: I kind of assume it would automatically assume any subfolder under a media folder is included.