I know about that regulation. We all know about that regulation. However, such regulation will not stop "some" captains allowing the nurse to "practice". The captains have stated that they prefer dual controls so that the nurse can take control in case of captain being unable to fly. Question is, when will the nurse be allowed to practice landing? Only chance to do so is during an actual HEMS flight (possibly back to base after service).
A regulation prohibiting dual controls will fix the problem, allowing dual controls but not allowing nurse to touch them will not fix it, as I, and most of us, know for a fact that the captains will want to teach them basics.