2003 server: how to mask a network drive as a local one to a backup software ?

A legacy backup software let me choose only local drives, not mapped network drive.
I would like to backup the content of a shared folder on a remote computer.
The backup server is a windows 2003 so I don't have symbolic links available through mclink.
Already tried subst for creating a virtual drive, but it is not seen by the backup software.

What else can I try ?

Probably iscsi should work but it is not an option for me.

Thanks

Filippo