I'll se if I can find some pics. or make another and post a video.
They are not that hard to make.
Think:
Dowel (of the material of your choice) that fits
almost snugly into the molded in rod-holder.
drill a 5/16 hole through center from end to end.
Cut it on a diagonal from near one end to the other.
Fix 1/4 -20 all thread to bottom and insert through hole to extend 1/4" above top half.
ram ball will thread onto rod and pull halves past each other and wedge into hole.
To remove it, unscrew the ball a few turns and rap it sharply. wedge will loosen and remove easily. ( thats my story and I'm stickin to it. )
Like any recipe, adjust it ( materials, sizes etc.) to your taste / needs.
Here is a quick model that is easier to understand than my ramblings.

I might make a mold for them if there is enough interest.
Good luck, Phill