If it is just for aesthetics, fill the void with al filled epoxy. Gray JB weld will probably work too. Clean the void with acetone, then clean it again. Fill the void and smooth it with a plastic scrapper. There should only be epoxy in the void. Works on carbon masts too.

This is mainly for Rolf. Instead of using an Al plate to protect the mast you can use centerboard gasket held in place with waterproof duct tape. Layline showed this for a monohull but it works for the Tornado. I used a ~15cm strip of centerboard gasket. I glued it down with contact cement and then taped the edges with waterproof duct tape.