I don't have an answer to the question but the suggestion to add a gyro to the rudder channel made me think of my experiences with full size aircraft. What is being suggested is effectively a 3 axis auto pilot with the roll and pitch channels switched off. I have been wondering if rate gyros could be employed on all three axis so that losing sight of an aircraft by reason of distance or cloud wouldn't hazard the craft. Likewise such a device could automatically compensate for any external disturbance and bypass the need for visual feedback and pilot reaction to correct any deviations. I expect that someone somewhere will have tried, discussed, and perhaps discounted the idea.