There's nothing that Tableau provides out of the box but I'd do following.
First, download affected datasources (or workbooks) with tabcmd. I don't know a good way to identify ones you need. Datasources view in 9.3 has "Connect to" column that list file name but I'd also look into querying Postgres backend.
Next, use some scripting skills to process workbook and datasources and modify their XML directly via simple string replace. Downloaded files will most likely be tdsx and twbx file - you have to unpackage them first (it's just a zip file - 7-zip command line tools can tackle that).
After you fixed up XML - publish them back with tabcmd.
XML part you should target is this:
<connection class='textscan' directory='\\SERVER\share' filename='file.csv' >
And here's something that might give you extra ideas: