Control of insect-scale flapping-wing robots is challenging due to weight constraints and inherent instabilities. Instead of adding more actuators to increase the controllability of the flapping-wing robot, we use a single actuator to drive a system of mechanical linkages to cause bilaterally asymmetric changes in the wing hinge spring rest angle of the left and right wings. We show in simulation that such a control input can generate wing motions which produce yaw and roll torques. A kinematic model of the mechanism was developed and an at-scale prototype of this concept was built. High speed videos of its wing motions are consistent with the kinematic model and according to the simulation, are capable of generating adequate yaw and roll torques for attitude control.