Would it be possible to use the back of a spectators hand for the change in believe? Would it be possible to have the spectator hold the deck in one hand, then place the piece on the back of their other hand and be able to do the change?
I did it this exact way tonight. It's the first time I've done it on a spectator's hand (usually done on a surface or table); tonight I lacked a table and needed something to perform completely impromptu. Believe was the first thing to come to mind. The reaction was amazing.
For the safest route, a table (or any surface) is best, but yes - it can be done. Note that this way is not taught directly in the video, and is definitely not the safest way of performing it, but as long as you have some sort of surface on which the corner can sit, you can pretty much do it to it.