Remote media server on backup network

I have an interesting scenario

In a remote site i would like to create a backup network and the clients and media server of that site will have a NIC on that network. i wont all backups from clients to media to go through the backup network.

The caveat is that that the master wont have access to the backup network.

Here is the example

Master

master01 10.10.10.5

Media

media01 10.10.20.5

media01-backup 192.168.1.5

clients

10.10.20.x

192.168.1.x

The master has access to the 10.10.20.x network but not the 192.168.1.x how can i make sure the backups are going to media01-backup?

can this be done with preferred network?