This still works? I remember doing this on Mw2-Mw3 for messing around, aka want-to-be Faze 1337 trickshot lobbies for kill cams.So you want to play your friends in a free for all online lobby?
The way I used to do this on previous games was. :
Send your friends all game invites - Tell them not to join - Search for a FFA match - Make them accept the invite as soon as you search for a game.