During training classes, if I feel that a student is doing well enough; I have them practise several engine-on deadsticks.

Then at random, while they are flying the plane on the buddy box, when they get to a good altitude, and in a safe location, I'll drop the trim and throttle, then flip the trainer button off momentarily to kill the engine for a real full deadstick.

They barely notice it happening...

I then say " it looks like you have a deadstick... ", what are you going to do.

If they hesitate too much, I then start indicating what they should do, giving them a string of slow directives until the plane is down.

Usually they are relatively calm through the event because of the directions, but the experience of having done it at least once, is a great confidence booster.

I have yet to loose a trainer this way.