Identical to the method for April's Loft, Strategy, & Turtle Soup:
Start a local (single-player) game with the account earning the achievement, which I will refer to as primary. Using a second controller, join the game with a guest account which I will refer to as secondary.
Immediately let the primary account die. Having only one turtle present will make it easier to fight your way up to Traag & is part of this sure-fire method for getting the achievement. Fight through the game with the secondary controller up to the area just before General Traag (just after going down the elevator, dodging the balls, & coming out into the foot soldiers & pizzas). Re-spawn the primary account as the same turtle chosen at the start of the game, before entering the battle with Traag. When Traag enters immediately let him kill the primary account. Using the secondary account, attack the boss until he is one or two hits away from dying. Re-spawn the primary account & use either controller to finish killing the boss.
As long as the primary account is present when going into the area in question (in this case the General Traag battle), dies immediately, rejoins as the same turtle when the boss is near-death, and only gets hit once before the boss dies (can be hit twice in this case), the achievement will unlock. The damage taken when dying upon entry is not registered.
UPDATE: Bosses flash pinkish-red when close to death. Comments have suggested an exact hit count for each boss would be helpful, I will attempt to deliver this information in the future.
UPDATE 01/01/2011: Traag takes 38-40 hits to kill.