If you are worth 2 cents as a teacher you have already had them launch and fly kites, and practice releasing the kite to safety, reloading and relaunching, several times before trying this move.
But to help things, maybe when you pass the CL to their harness, you should have them put their hands on the release, not the bar, while you still have the bar.
"KEEP YOUR HANDS ON THE CL, OK?"
Then move the bar to where they can reach it,
Then let them put their hands on it INSIDE yours
-NOT at the bar ends-
Then remove your hands, after making sure they are ready to control the kite, and transfer the leash.
Should be good, if the instructor and the student have done appropriate basics first.
If not, do the basics first.