Rudder locked hard over and increasing airspeed will quickly lead to the situation where no amount of pedal-pressure can centralise it again, and if carried to the extreme, will probably end up with the rudder detaching, as the airflow impinges on the aerodynamic horn forward of the hinge-line. Those hinges are relatively flimsy.
Answer is, don't lose control of the airspeed with the rudder hard over! Reduce the speed, and pedal-power alone will enable you to centralise the rudder. My training (UK) in the early seventies did not include this demonstration due to the above, and it remained a discussion item, and as we did not operate into limiting strips, side-slipping was forbidden.
As for turning it on rudder alone, poppycock! Put the man back in a Tiger Moth and invite him to fly, keeping the ball centred at all times, and THEN have another go in the DC-3. It will all become crystal clear! It's called properly coordinated flying.