[THIN] Restrict access to local files accessible via published application

Hello,
I need help figuring out how to do this:
We are hosting a new application that is published for clients via CSG.
The application is designed the way where during the login they need to select 
a configuration file that is located locally on citrix server.  When they click 
browse to select the config file they can browse to the entire C:\ drive.  What 
needs to be done so clients don't see the C;\drive?  
It is restricted on the same server in Windows Explorer, but they can see it 
throught the application.

Your help is greatly appreciated.
Larisa.

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