Like learning how to fly or anything else, it will take a bit of practice. Funny thing, I never thought of suggesting that people use a sim to practice this teaching method. Many times, people have told me that they tried it once and thought that the buddy-box was better.

I have had many of my students hand the tx to a friend and very efficiently and safely give flight training. BTW, this was a week after the new "instructor" had his first RC flying lesson ever.
The trick is, whether you use a buddy-box or not, is to strongly suggest that the student not move the sticks while the plane is in straight flight. Those who use the buddy-box, you could give your student a little ground school to show them just how little stick movement is necessary. Give them some "dry flying" instruction for a few minutes before the plane ever gets in the air.

To show how stable a trainer is, sometimes I will lay the tx on the ground while the trainer is in the air and not touch the tx for several seconds, then reach down and bank the plane over and let it make the turn all by itself. I am sure that too many instructors make learning look much harder than it really is.
When I hand my tx to anyone, even a 4 year old, there is very, very little risk to my plane. I just tell them not to do anything until I instruct them to. Move the aileron stick over for a count of 3 and then back to center...and then wait until the plane is headed in the proper direction and then the other way until I say "center".
Keep in mind skeptics, I've been safely doing this for over 30 years. BTW, I am always learning.

Take care,
CCR
http://www.kites.org/rc_instructors