Because so much of backgammon can rely on the roll of the dice, it's not always easy to "cheat" with a friend over LIVE, but it can be helped along if he leaves as many single pieces around the board as he can.
Whether playing on LIVE or against the CPU (try the Easy setting), just break up your moves to target the single pieces as much as you can. Strategically place your pieces in pairs, especially in your home board, so that you can limit your opponent's moves and prevent him from moving pieces off the bar. Once you have four on the bar at once, the Achievement will unlock, even if you have not yet finished the game.