I think you can set it up at your office with the IP address it will have at the other network. If you configure DHCP services, make sure you set it up for the other network also. The Fog server will not function at the office, i.e. you can’t really test it by imaging/registering computers, but you can once you get to the new network.
I would probably choose to set it up in the current network, verify it’s working, then move it to the new network by updating the IP address via the wiki article linked in Roberts response. Deploy the server and troubleshoot from there if needed.