First of all go in to Forge pre-game lobby and press X. This should bring up a settings screen.

From there set damage resistance to 10 or 50, with base player and lead player.

Then go into Forge and make four shield doors in a square shape, then put a football inside of it.

The next part is easy - put down a turret next to the shield doors and set it to instant respawn.

Once you have done that run into the football box until your shields are flashing red, then quickly run out and go on to the turret, then rip it off and you should die, but when you respawn there will be a clone where you died.

PS: This may take a couple of tries and if you are playing over Xbox Live sometimes you will not be able to see the clones.

PPS: Works best on Foundry.