Beyond the "what'ifs", it is certainly a way forward if the tendancy is bad enough and Billy doesn't have the time or inclination to get the laser meter out, or mount the plane to a flat table. The idea of mixing (in this case) is to reduce the pilots workload.

If the model is yawing off in level inverted flight, it is probably not tracking straight either in negative pushes either (probably corkscrewing in negative loops), where in this case the mix is still valid- reducing pilot workload.
Jim W.