Filter Umenu to only display Prefix Filename

Hi there! I'm trying to create a patch that populates a umenu's items list only if it matches a filename prefix. Ideally I would be able to change the prefix word it populates the umenu with so I can switch between only seeing files that start with the word "idle" into seeing only files that start with the word "action".

I've tried the regexp and substituted the irrelevant words in the file name to leave only the prefix and the id number but then I can't find a way to either populate a umenu or have a jit.qt.movie read the files once the files name has been stripped.

Thanks in advance!