I tried it:
It didn't really work for me. That's not to say it's impossible, of course.
I turned an old snowboard into a sandboard by adding straps and a formica bottom. All sandboarders say that formica is the best material for them. The normal snowboard material just won't do.
First thing I noticed: getting moving on sand is hard. The friction just kept me glued to the spot until the kite was pulling above a certain threshold, and when it happened I basically zipped away with no control. After which I couldn't edge for the life of me, and most of the times the board got stuck into sand after a few meters.
Also, the board's reactions were extremely dependant on the type of sand (coarser or finer, wet or dry, etc...). Sometimes I could slide much better with my bare feet than using the board - other times I got going full speed until I got into a slightly rougher patch of sand - and then the board just stopped dead in its track as if it had hit a brick wall. Also, the type of hard sand that I could slide very well upon made it even more difficult (impossible?) to edge. I just ran straight downwind without any control of the board. I had some fun going down dunes with a small kite, but all in all I felt like it was more pain than pleasure, and exceedingly easy to break some tendons.
I actually don't mean to discourage you.
Some people do use sandboards with kites, so it can be done. I know that sandboarders routinely use some kind of special board wax, and that might help. The straps position I used was clearly wrong, and that surely counted a lot. Adding some kind of very very small fin might help keep the board straight (but it won't help you to edge). Also, I think that there are places in the world where the sand is just ideal. I can only guarantee that they're not anywhere near my home.
Whatever you do, please try it underpowered at first. I used a small 3 square meters trainer in about 15 knots.