Without resorting to hacking the DNS-323 to extend it's capabilities, the only way to back it up is through the network to another device.
Since your boss is asking about disaster protection, which is actually a much more complex issue than just a backup, I'd say you're looking for some form of offsite storage - yes I did see the piece about a fireproof safe, but I'm not betting on digital media or electronics surviving the elevated temperatures - so I think you're looking at removable media.
I want to mention here. that there are companies who offer "online storage", one example is Mozy, backing up your DNS-323 to such a service may be an option for you, but, living in a country where internet bandwidth is both expensive and unreliable, these are not my first choice.
So - where does that leave us - I hate to say this, especially on D-Link's forum, but perhaps the DNS-323 (or any NAS for that matter) is not the best device for your needs, how about a removable cartridge drive such as the Imation Odyssey and a rotation scheme that features cartridges being stored in the owner's home or a safety deposit box at a local bank.
Uhh - D-Link - support for a removable media USB drive enclosure such as the Odyssey and another screen in the web interface to allow backups would certainly meet this user's needs.
Hello? D-Link? Can you hear me?