[Since my previous post was five years old, I hope you'll excuse my rather tardy reply.]
By "symbolic link," I was referring to UNIX-style symbolic links, which can be created on most UNIX-based systems (I was doing this on Mac OS X, but I'm pretty sure it would work on most Linux variants as well). If you have direct shell access to your server, try typing "man ln" to get the man page for the ln (link) command for your particular system. Then you can find the precise syntax to use to create a symbolic link. On Mac OS X, for example, I would type...
ln -s [source dir] [target dir]
...where [source dir] was what I want to create a symbolic link to, and [target dir] is what I want to call the link target (i.e., what will point to the original source).
In this particular case, I would want the [source dir] to be the common folder for the teacher (the single folder the instructor would access across multiple courses). So I would replace the individual folders Moodle creates for each course with symbolic links to the single shared folder.
Hope this helps.