I don't want why you want to do that. Anyways thats not the problem. What I can figure out from your mesasge is that you want to keep an offline backup of some folder in you pendrive, right?then rather than running your script manually everytime after plugging that USB device, why dont you put that "run script command" in the udev rules itself. I bet this will make life much easier though you've to put some effort initially learning udev, but it'll payoff in the long run.
Secondly, you dont want any message to be displayed whenever this copying process is going on, right? then just remove the notify message that is available in the .rule file in /etc/udev/rules.d/ directory meant for your USB device. Just learn how to add/modify these rules then you would be writing off nice rules to take backup or anything you like whenever a new device gets plugged.
For udev you may like to start here,
Hope it helps