Using SuperDuper for an offsite Time Machine backup

[toy]

I have tried to use SuperDuper to maintain an offsite backup of my company's Time Machine backups.

The setup is simple: At the office, I have a Macpro running OSX Leopard Server and an attached Drobo external harddisk for Time Machine backups. On the Drobo, a Time machine backup of the server itself is maintained, as are Time Machine backups of all company iMacs and MacBooks.

Thanks to Leopard Server, this setup works wonderfully well, but has critical drawback: the backups are stored at the office. If something happens (fire, etc.), I still will lose all data.

So, I've been looking for solutions to maintain an offsite backup of the Time Machine backups on the server's Drobo drive, this is the solution I thought of:

Office: Macpro with OSX Leopard Server, VPN server, Drobo external drive with Time Machine backups (of server and clients).

At home: iMac with OSX Leopard, VPN client, SuperDuper, Drobo external drive to store backup of office Drobo.

Every night, the iMac is scheduled to wake up, opens the VPN tunnel to the office and mounts the office MacPro's Drobo.

So far, I haven't been able to copy or sync the office MacPro's Drobo with the iMac's Drobo.

The problem is: Drobo doesn't see the mounted MacPro Drobo (I also tried to make an alias, but that does not work either).

The question is this: is there a way to force Superduper to work as described above, or do I need to use alternatives, like rsync or online backup services?

Any thoughts are highly appreciated.