This is the way I do it and it works so try again if it doesn't work for you.

1) go to custom games create a free for all game with the map you want to play and set points/time limit to unlimited
2) save that file and back out
3) hover over custom games click y and join a friend who is in create a class menu
4) spam a very quickly.
5) if done correctly then it should show public match with a 0 next to your name.
6) make sure to have a total of 6 ppl in the lobby (so invite friends)
7) click cod tv go to friends feed and click on a friends snd file
8) quickly back out and make sure to click bring party
9) now invite at least 2 more ppl (total of 8)
10) the game should start

Also be sure to follow me on utube MrHiddenfreaks