Due to the fact that the ski-sand friction exceeds ski-snow friction, it's not possible to use long skis on the sand. The torsion forces during turns would easily hurt, or even injure, your knees. 

When you use ski-material in the sand you should take the 'polishing effect' of the sand into account. Only use old ski-material, which you don't want to use in the snow anymore. 
I think bigfoots or snowblades would also work well, but I didn't have old ones available.
The following steps will show you how to transform your skis into skites.
 
 

Step1 Take a pair of old skis (often available for free at rent-a-ski when you tell them your kite story).
Step2  Use a steel-saw and cut the skis into three parts.  Lengths:  Front-part: 87 cm  Mid-part (where binding is attached): 55cm  You won't use the back-part.  Please use the same cutting lengths for the left and right ski.
Step3 Remove bindings, clean the skis properly and paint the top of the ski if you want.
Step4 Glue the mid- and front part of the skis together and give the glue some time to dry! Drill holes through the skites and connect them with M6-bolts  Please remove parts of the bolts, which are sticking out to prevent injuries.
	Here on the left you see my own skites. You can see clearly that the shoes are posiotioned towards the back-end of the skite.
	Here you see Rijk wearing his 1st skites. The NATO-shoes are fitting perfectly on the skites. Thanks for the pictures Rijk!