^^^ This is how most keel boats store all their sails and as long as you don't press the creases in won't do much damage if done once. If you want to protect the sail even more. Lay an old quilt or blanket on it and fold it up with the sail. This will stop the creases being flattened.

Second thought what does a return flight to the mainland cost? You could always check it as oversize luggage.