Here's a couple of suggestions. The leading edge could be made from Balsa wood. Coat the inside of the balsa wood cove with a sanding sealer to close the grain. Then, attach the the balsa to the aluminum flap with contact cement used to attach counter top laminate. Sand your final shape in the balsa then coat with varnish. When you cover the aileron in fabric and shrink it down the fabric will help to hold the balsa in place. Balsa has been used as fairing material for a hundred years so it should work on a Super Cub just fine. Just my thoughts and ideas.
Psalm 36:7 "High and low among men find refuge in the shadow of His wing"
What do Just Aircraft use for gluing the wood ribs to the aluminium spars?