To keep my external halyards from slapping, I took a stanchion bullseye and mounted it to the grab rail by the mast. Then I made a rope grommet from triple braid through the eye. (The twist in this pic is inadvertant, but I'm just not anal enough to go untwist it for the picture.) There's one on both starboard and port sides.

Spare and unused halyards clip down here, and by cleating them off hard they don't slap inside the mast either.

The cool thing about this is they don't interfere with the pole, so they can just live there until needed.