You can practice using this method on the sim and/or when flying your own plane alone, you can hold the tx over like your student was holding the tx. This way you can get used to the wierd angle that your fingers will be on the sticks. You can extend your sticks and practice flying with you thumb and forefinger right down to the bottom of the elevator/aileron stick (mode 2).

The first thing I tell my students is to do nothing and just watch the plane fly very smooth, straight and level very well on its own.
Then it's one movement at a time, like moving the stick over about an 1/8 of inch for a count of 3, and then back to center.
The trainer will bank and turn mostly on its own as in without another stick movement for perhaps a count of 8-10 seconds as it makes the turn.

I've noticed student's fingers dancing around like crazy and the instructor being completely unaware while being taught on the buddy-box. I can tell a recently graduated student by they way she or he can fly reasonably well, but their fingers are still mixing a batter. I guess they figured that they can get the plane up and down with gittery finger movement, this must be the way to fly.

Yep, practice using this method on a sim and you will find that you may only need to have your fingers assisting your students for no more than 5 minutes, tops.

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