Counter rotating props would work get. I am a professional pilot and have been flying R/C for one year. I would suggest adding right thrust. It will take care of your yaw at all speeds. You can cheat with the rudder but now your plane will be crabbing all the time. Try moving your rudder trim three clicks left. You will have to add aileron trim to offset the rudder trim. Your plane is now out of rig and that is not good. Remember you need up or downthrust adjusments for different spped right? I would have to think it would be the same with right thrust. For you experts can you mount your engine just left of the vertical centerline to add right thrust? I think this would work, but I am not sure. I saw a picture of a U-CAN-DO-3D and his engine most of been 5 degrees to the right. It did not look very good with a cowl.