Create a backup job using wbadmin specifically with the
-backuptarget switch i.e.
wbadmin requires the share to be a UNC path, so other network storage filers are excluded. But really, did you want to push your backup across a network using FTP? Of course you didn't. When asking yourself "Can Windows backup to $n storage service?" reverse the question and ask "Can $n storage service be presented to Windows as a local drive or UNC path?" If the latter question can be answered in the affirmative, then you can use
wbadmin to backup to it either locally or across the network.
If you're more into PowerShell (which anyone administering Windows boxxen should be), have a look at how to add PowerShell cmdlets that can manage Windows Server backups. There's quite a gamut of them:
It should be noted that the PowerShell cmdlets do not support backing up to removable media. You'll need to fall back on
wbadmin for that. They do, however, support network targets.