I leiu of a Visclamp, you can use a local, round rock (or pine cone with a sturdy tarp) and wrap cord around it.
As long as you didn't step on them, ping pong balls are surprisingly tough (consider how hard they get whacked in play) and are as light, spherical, and smooth as you can possibly get. Wrap a cord around the base or you could make the oblong peanut-shaped thing out of coathanger wire. I'd suggest making a jig with 3/4" and 1-1/2" dowels to give that nice smooth curvature.
Dang, that's a good idea - I might have to get back in the garage, clean up the bandsaw blade project and knock some out.