Assuming you're happy with a disk-only based backup, then there are a few ways You could do it.
If you have a backup-to-disk folder on your server, and another folder which is mounted on your BE server, but located remotely, you could define a second set of B2D folders on the remote disk, then add a duplicate job to the backup policy. Pros: Easy to configure. Works out the box. Cons: On a slow link, mounted drives can have poor performance. Also if the link fails, the duplicate job will fail.
Another option might be to use Replication Exec to replicate the B2D folder to a remote location. Pros: more reliable over slow and transient links. Cons: Requires extra software.
You could also investigate using CPS to copy data to the remote location.