Creating FTP accounts outside a virtual server's home

I currently own 4 servers and I'm trying to setup a backup system where, for example:

• SRV 1 backs up its files on SRV 2
• SRV 2 backs up its files on SRV 3

and so on, basically every server backs up its files on at least one different server

The problem is that I have only found GUI options that let you create a "backup" user with a directory inside another user's home directory, so:

what happens is that SRV 1 backs up its files on SRV 2's home directory, but when I back up SRV 2's files, they also include the backup from server 1, and it rapidly becomes a huge backup :)

Is there any way I can set up a new FTP user without being inside a virtual server's home directory?

Thanks