When I plug in a USB-flash-stick, lsmod shows as extra modules:
> nls_iso8859_1 12713 1
> usb_storage 57199 1
So, how about disabling (the loading of) usb_storage? Maybe block it in /etc/modprobe.d/blacklist, or just remove usb-storage.ko from your system,
Or compile a kernel without usb_storage?
EDIT: tested it:
Unplug usb storage sticks.
at the end, add:
sudo rmmod usb_storage
sudo nano /etc/modprobe.d/blacklist.conf
Save and exit.
Now plug in a usb stick ... and see that it does NOT work ...