I'm not sure if you know a program called, "Radmin VPN"
This program allows you to use the local IP address, to connect to different computers through the network. It is possible to play with LAN network cooperative games, but on all internet. It is only necessary to download the program, set up an account with an email and password, share the virtual IP address of the account with whoever wants to connect to your computer...
I have not tried it yet with BoD, but I will use it when I manage to program the "Cooperative History Mode".
So, for now that should be useful for network play with the "Arena Mode".
If someone manages to play Arena Mode with that program, Radmin VPN, please comment here to know that it works.
Sorry, I am not sure if the use of such a program is safe, because suddenly a new Ethernet network is created, which I cannot control; and also, a "remote desktop" program is installed that fully accesses the computer... So I have uninstalled it until I get to know how it works without hacking risks.
Another thing I saw, is that there are many "game networks" in which there are many players. But I didn't see any room for the BoD game... so if someone manages to create a shared network for BoD, without the risk of being hacked, it would be great because anyone could play Arena Mode, on the entire internet.