Multiple file directories

Hello
I need to give different users access to different directories to use/upload images and doc files, depending on a variable that is read at login.
I have tried to pass that variable to the file filemanager/connectors/php/config.php so it can modify the global variable $Config['UserFilesPath'] and spread the change through all the script.
But until now it has been useless.
How can I do it, so the base file path for images and docs is NOT the same for all users?

Thanks
Vladimir