Just a thought... But how about stips of a light wood ( Like Balsa or bamboo ) drill holes thru the edges run a small nylon cord thru it tie it on both ends to hold them in place and then another cord thru a vertical hole on each of the outer strips tie iton one end and on the other use a cord-lock (like the ones on winter jackets) I would also dip the outside edges of each of the strips in rubber so they don't slip...
Or was that what you were thinking of doing already?