have them host a custom game and you join in after the game has been started
It's best to do it on a custom game (regular, not easy) anyway because that way if someone drops out, you can get someone else to join and complete the EE. We had 2 people drop out on purpose and one who got disconnected so we were able to pick up others to finish it.
Sorry for the bad english, google translator sucks
It's a way to do this but I think it would be kind of drastic, you could delete the information from the COD of your system (or remove the device where it is stored) and see if the tower was turned off, maybe it works, if it does not work, I do not know what to do.