I have never had any problems pulling the mixture back on a fully briefed student to simulate engine failure on the runway.
It is the only realistic way to do this exercise as the student should have a good grasp of the throttles ready to retard at the first sign of engine failure and it is difficult as an instructor to get a hold of a throttle. At recovery a full power check should be done before proceeding with further flying.
I seem to remember the CAA recommending not to pull mixture on climb out! Who would? We have all heard of instructors who do, the same ones try and do touch and goes with a cold engine
following sim. asymmetric landing.
Unless you are above 3000 feet then the mixture should never be pulled and in any case it is pointless as an exercise as the student can see which engine is going to fail. Much better to shut off the fuel.
My mag experience was as a rear seat pax awaiting my turn in the front left seat whilst type rating training on Seneca.
This was the students 3-4 hour in twins.
We were at 4000 ( and descending).
The instructor was ex airline with a zillion hours, sometimes you can't stop a student doing something you don't want him to do.
Brief, dry run and well written checklists are the key