File Browser: only list certain fille types...

I know there is probably some way of doing this.. and I have tried to read through the forum etc..

What I am trying to do is:

FILE BROWSER:
1. I have set the FILE resource to look at a certain directory.. no problems, it shows all the files in that directory.
2. I need to show only certain file types of that directory i.e. only *.txt for example

I realise I could possibly move the files to another directory and list them all there, but due to constraints of an existing
setup, I need the above to work.. I have checked the file browser config and of course the normal config.. I thought
at first that the allowed extensions was it.. but of course this is for the upload etc...


Any help very much appreciated!