1.have friend inv u to player match
2.have friend change to private match than combat training
3.then friend must back out
4.u inv your friend back
5.u change lobby to wager than to player match (quickly)
6.then u back nout
7.got to private match
8.change map to nuketown
9.change game mode to search and destroy, then put in on unlimited lives
(keep time at 2.5 mins or it wont work)dont change weapons or killstreaks}
10.hover over the health and lives button
11.then have friend inv u back
12.have friend back out and inv him back the game should start.

When game is over you might not have your xp its like a 50/50 chance i havent figure out a sure way to keep your xp yet.

Also if it works and u want to do it again u have to go back to the main menu EVERYTIME.

THANKS & REP