I used this to backup usb drive attached to desktop
I don’t know if this will work but I don’t see why not
As long as the drive letter is the same it should work
Simple really
It seems the only thing stopping you from backing it up is being able to select the drive letter
On my workstation my USB drive is drive L and on another Workstation we needed to backup there G drive
So I set up a work station and I partitioned a drive with the corresponding drive letters
I needed to backup G and L
So when I created the backup policy drive G an L is in the list of drives to backup
Scheduled the weekly backup and it works