There is a non formal way I used in a wiki page.
You use the syntax to link an external page.
[http://Your Host/Your Tiki Directory/tiki-download_file.php?fileId=X]
Your Host = Hostname or IP address
Your Tiki Directory = Name of the directory where Tiki is
X = File Id (You can find the ID from the Tiki Database or when your mouse pointer is over your file in the File Gallery).
This is not recommended of course for many file links and it's a little...adventurous.