Link to internal file shares within posts

I have searched for 2 days using Google, the WordPress.org search, and even Bing (I was desperate :)) I am in search of a plugin or method that would allow my users to include in their posts links to different files that were sitting on internal file servers. Most of the file servers already have proper permissions and this is all running on an internal WordPress site with no communications to the Internet. Basically a glorified Intranet and I really would like to provide the ability to post links that included file server docs but can’t seem to figure out how. I read about modifying the formatting.php page which I included ‘file’ but it doesn’t appear to work. Plus, upgrades would probably break that and so if a plugin of some kind was available that would be great.

Thoughts?