Call one of your player's over with the call "Follow me". Call him over to one of the wooden crates and say the phrase "Need backup or taking fire... need assistance". He will guard you while you attempt this. Shoot the ground just in front of the wooden crate and jump twice. One enemy will appear from either your left or right. Kill him with your hand and say "follow me" and repeat the process, all up to the point where you jump twice. You will then be invisible. This only works under the expert difficulty setting.