Playing "Online" games while offline

I have been trying to get into a certain online game while offline (I have definitely seen multiple people accomplish this). I made sure the console was set as my Home Xbox, as well as restarted the console without going back online. Usually (while offline), I will receive the Xbox "You need to be online for this game" message a few times when I try to launch the online game. However, after trying to launch the game again several times, I will stop getting this message. For a minute, it appears as if the game is launching normally, with a loading screen and everything, but just before fully getting into the game, I receive an error message, except this time from the game itself, not an Xbox error message. I am sure the game in question has certain ways to play that are completely single-player and with no matchmaking of any kind involved, yet I continue to receive an "Ethernet disconnected" error message from the game just before getting in. I understand that this may be a more game-specific issue, but if there is anything that can be done to access an "online" game normally while offline, please let me know. I have seen many others access a game like this legitimately, so I am quite confident this is possible (I only intend to use fully offline, single-player modes in this game, if I do successfully launch it while offline).

:)