Threre are many mast head floats available but here is a idea for something cheap and removable.
Take a small diameter line and tie it to the top batten pocket. Add a short piece of swim noodle. Run the line through the sail masthead plate/grommet, add another short swim noodle and tie off on the top batten grommet. Not exactly areodynamic but.......
This should be enough additional flotation with an air tight mast to keep any catamaran from going turtle.
Cheap and removable for Hobie Class racing.
Any other ideas?