i would suggest splitting the defesive area you would like to use into boxes with only one player allowed in each box at a time. starting from inside the 25 yard line till maybe another 5m beyond the 25. each player must use a triangular pass to pass to the player in any box, and the player without the ball moves to a box with no player to simlate a run off the ball. remdind the players that this is a game situation and to always cover the ball before passing, therefore simulating a defensive player in there mind. you then can add a defender.