use a cardboard cut out of a board and use the whiteboard to draw the waves/ocean. Then use the desk to show how to paddle and pop up. It surprises the class that you are actually standing on the desk and demostrates your point. If your good enough at teaching, they will get the point. I did this for my public speaking class in college and got an A.
a VIMEO video of how to surf, then mute it, and put your own words in it. youtube sucks and is terrible quality. also, bring a sticky bumps candle and light it so you have the fresh scent of wax spreading across the room as they watch the vid. You could always punch people in the stomach then throw ice water in their face and say "this is what it feels like to **** up on your drop in in the middle of winter".
Yep Yep.... Beginners video with your narration is the best way to go.