Use the mixture and have a realistic training scenario, managed risk with a well trained and competent instructor.
The instructor involved with the Duchess practice engine failure (mixture cut) fatal crash was quite experienced with over 30,000 hours and the Boeing 767 Air Canada captain in the left seat of that Duchess undergoing the instrument rating renewal was less experienced with only 16,000 hours...
So now about this "realistic training scenario, managed risk with a well trained and competent instructor"?