Sit on an erg at the catch, but not holding the erg handle. Instead, for sculling boats, hold a one-pound weight in each hand in a sculling catch position. (For sweep boats, could try the same with either the same weights or some sort of short, light bar.) Play with slight leg movement from the catch back to three-quarters slide, focusing on good, stable posture. Do this for three minutes, then take a three-minute break, then repeat.