|You really aren't talking backups. Backup to tape/DVD across a wan is...sloow.|
It is a different thing to have a backup library on a different physical network locally then across a wan link. Even locally the backup is going to tie up the server being backed up whereas imaging is quick.
Volume shadow copy for instance. We never notice it on our servers when it runs.
Better strategy is you have an image server locally. At regular intervals you image your systems. Images go to the image server that then mirrors that image to the other end of the wan link to another off site server.
You can always backup to tape the image without impacting your regular network at all by having an attached tape system to the image server.
There are a number of vendors and different ways of approaching this with both hardware and software.
Google is your friend