Dang, a DIY rope is pretty cool!

Unfortunately, the closest I could find was Buddy Lee's swivel system they use for the Aero Speed and Ropemaster: https://www.amazon.com/dp/B00GNJ5JGM/ref=cm_sw_r_cp_awdb_imm_J3NBJSYNH9VXS07R7016?psc=1&vs=1

I'm not sure if that would work with what you have because it's meant for PVC with a certain size hole in the middle and assumes you have a certain type of handle and fastening tool.