All you have to do is go to survival in Burger Town on two players.

Get one of your friends to get the grenade launcher and the dude you want to sling in the air gets what guns he wants.

Make your friend get behind the starter button. Your friend gets on the button and your friend jumps on top of you and before you hit your friends head your friend shoots you, but when he shoots you what you need to do is hit 'A' when he hits you on your butt.

Then you need to move while in the air and get on top of the Burger sign.

Get your friend to start the button but watch out for the Spitter because it can still hit you.