I’ll try and recall what I did with my Tivos.
Location 1, where I guess your main 360 box is located, is configured with DHCP operating and also has a Openvpn server. That server is configured with a TAP configuration. Assume for the moment that the LAN address of this router is 192.168.1.1, and the DHCP server is configured to hand out addresses from .50 to .254.
Location 2, where the mini is located, is configured with an Openvpn client on the router exported from Location 1. The router has DHCP off, but has a LAN address manually assigned that is on the same subnet as Location 1, but in the .2 to .49 range. The Openvpn client is configured to start on boot. Note that the mini, if it is plugged in, won’t get an IP address immediately. Maybe it has flashing lights, or smoke, or something.
Now maybe, when the router at location 2 starts, its openvpn client reaches out and forms the bridge (TAP) to location 1, and the DHCP request emanating from the mini is negotiated with the Location 1 router. In that case, it may also then bonjour with the main 360 box. It may also be that other devices at location 1 will now get IP addresses and send traffic to the internet over the bridge and out your location 1 internet connection. That is as good as you are going to be able to do.
Now the bad news. Even if the mini connects, it could very well be sensitive to latency or speed, and sense that it is not on the same physical network, leading to a disconnect, usually exactly at the best part of what you are watching.
Note also that all level 3 traffic is also going out back and forth over the bridge. Also, whatever the download speed is at location 2, your internet traffic is going to be limited by the upload speed at location 1. If the bridge goes down, all of location 2 goes down and you will have to completely reconfigure things while the family is screaming at you.
To avoid this, I think I might have set this up so location 2 had its own DHCP server running, with location 1 and location 2 having different ranges, and then blocking the DHCP port so those messages didn’t traverse the bridge.
Drove me nuts.