Just take a flat elastic such as woman's hair rubber, fold it in 2 half loops (like a moebius ring) to form a 8 shape. Insert each squeezed ball in each half loop. Pull on the skin... Et voilà !
I used a silicon rubber (the kind girls use to attach hair in the shower). Tension is ajustable by elongation, so it is easy to wrap around balls without sliding.
It gives an outstanding shiny look to the tensed balls skin, and pressure boosts pleasure arousal...