You should really be able to put that together quite easily. To try a build a bow, but be stuck on the gizmo, just cant be allowed to happen. Try again - - please.
Take a 6 inch by 3/4 by 3/4 peice of pine and drill a hole dead center for a pencil and conter sink to back side for a nut (maybe 5/16), which you can epoxy, or Jb weld in place. Once dry, screw a pencil thru the nut and you are done.
when using, I keep my finger on the end of the pencil to keep it from spinning in the nut - but only if the pencil is a little small for the nut. You could just get a fatter pencil.