Filter the lobby in a way that it contains only rooms within the Local Network Area

I want that all player of "Internet Caffe 1" can see only games made by players playing in the same "Internet Caffe 1".
I can not just use the custom server name as there will be multiple Internet Cafes using the same game version.

I don't have anything against multiplayer is handled via the remote Photon Cloud Server, I just want to filter the games in Lobby.

What is the correct way of solving this?