We just tell the "HAL" not to mount any USB storage devices.
I created a file under "/usr/share/hal/fdi/policy/10osvendor" called "99-ignore-usb.fdi" with the following contents
<deviceinfo version="0.2">
<device>
<match key="@block.storage_device:storage.bus" string="usb">
<merge key="volume.ignore" type="bool">true</merge>
</match>
</device>
</deviceinfo>
