Thank you for the reply…
…but that’s not exactly true 
Solution (for people with some linux knowledge)
Go to
http://IPaddressOfMyBook/UI/ssh
Enable SSH (turn it back off when you’ve finished).
Using something like Putty (or other telnet/ssh client), login to the MyBook using the details on the webpage screen.
rsync is installed which you can use to transfer between the MyBook and the USB storage using;
rsync -r --progress /src/ /dest/
NAS data can be found in: /DataVolume/shares/
USB Data/target can be found in: /var/media/CUSTOMSHARENAME/
Works a treat 
