Spool for tennis ball cannon string

This is a spool designed for SpiderWire fishing line that attaches to a tennis ball for launching into the air. It clamps onto the 2.5" schedule 40 PVC pipe (cannon). The actual intent of this is to hang HAM radio antennas into the trees.

There are commercially available spools that are designed for bow fishing, but they are not common and need some additional hardware before they can fit on the PVC pipe.

There aren't really any overhangs, so this should be a fairly straightforward prin