Actually I'm thinking of something else, I've known about (much cruder) versions of this for a long time but what I heard about a couple years ago and then never again was an early prototype of a system for adding 3d tactile sensations to touchscreens using a similar approach.
Unlike many of these clips, the creators were kind enough to provide a short abstract of previous work. So you can see the idea is an old one. There is a demo of the '75 work at one of the science museums in the New York area; basically a horizontal tube with a loudspeaker to drive the whole into a standing wave resonance. small particles inside the tube rise up in the nodes of the standing wave and levitate as seen here.
That's pretty brave. At those sound pressures I might expect to see cavitation in a fluid, like your ball sack. In fact, Putterman et al claimed that in a spherical resonator ( like each of your actual nuts ) you can get shock waves in the center that trigger tiny fusion events. You'd have a little fusion reactor in each ball. It might hurt a bit; but SCIENCE!
Also, what if these 'spherical' resonators are more on the oblate side? Or extremely on the oblate side? And what if one of them is a bit smaller than the other?