Go from the Shore
If you have sufficient depth of water close to a shore, or low jetty etc, you can set the rider up kneeling on the board, on dry land. The boat takes up the slack, then gooses it onto the plane. The rider simply leans way back, the board is pulled onto the water, and is up and running right away - dead easy! I have taught lots of kids and adults this method - its almost foolproof - the rider just has to make sure that the nose of the board does not dig in - else he will headbutt the water.
My youngest used this method for his first try on a kneeboard. He was about 8 yrs old then. We set him up on a jetty covered in rubber matting, about 6 ft back from the edge. A bucket of water was thrown on the matting to lubricate it. The boat pulled him off, a drop of about a foot, and he was up and running - no problems.
A sandy beach is easiest, tho I have pulled people off rocks (scratches the board though). A bed of seaweed can help to smooth/lubricate takeoff.
Remember to instruct the rider on how to release the board/strap when he comes off/dismounts.
Have lotsa fun.......
"Remember the Plug!"