The traps need focused retraction and depression work to prevent imbalances. For this exercise, start in the regular seated row position while making sure the back is arched and the chest pushed up.
From here, squeeze the shoulder blades together and hold for several seconds. By focusing on pushing the chest up and out, the shoulder blades are more easily depressed.
Mike Boyle hates the question, "If you could only do one exercise, what would it be?" To him, it's like asking if Superman could beat the Hulk. Regardless, he gave us an answer that's pretty intriguing.