I've heard they use silicone spray, but I'm betting that Triflow would work better. Here are links to contact the Ranger at Great Sand Dunes NP. They ski the dunes there all the time. Either the ranger will know what they use or will know someone who does.
http://www.nps.gov/IMR/sendmail.htm?o=%3B3)%3F(NJ%2B%3AH%3AB1J0.]_%20.JN4^22*]2II_16!%22X%0A&r=/grsa/faqs.htm
http://www.nps.gov/grsa/index.htm
Definitely want to use crap skis. I would think that whatever you put on them to make them slide on sand will prevent the skis absorbing wax. Bases will probably be dead after, unless you can find something to totally clean it off.