Officially it cannot be accomplished. This desire to perform a remote backup to an offsite location has been discussed in previous threads. The unofficial workaround is to use SSH and then the Rsync command, and open up ports through the firewall(s) to allow the traffic through. Here are just two recent threads:
http://community.wd.com/t/help-new-customer-keeping-the-drive-at-another-location/161354
http://community.wd.com/t/automatic-backup-files-and-distant-bakcup/160633
