Thanks for making it "Scientific"
As you sought ideas,
Try using a Chi Machine or whole body vibration plate. The idea is to put your feet or ankles into the Chi Machine. Jiggling George is the one i use with enema. It works your legs left and right and sends a wave up your spine all the way to your neck & head. I like it with only a quart of my solution of the day sloshing inside.... Especially 1qt and a butt plug because my machine is not set up near the pot, of course. Even without the enema fun, it is great therapy.
But agar-agar balls with a pint of water might make a significant "scientific advancement".
To advance your tests, start with a thin pivot disk under your hips.
Try an exercise foam roller, as well, with 90 degree planar adjustments under the hips and turn it on!
And be sure to include all notes, please. 💦 💥
For me, i like to play railroad tunes and steam drawn train sounds with it, if you can imagine. Just don't get caught, aye.
Keep notes safe.
Back in the 50s - 80s and even now, one could plan ahead and get in a "small enema" ride with a Pullman compartment. Small was big, but with ribbon-rail tracks now days, the old "clickety-clack" on down the track is gone. Also with high speed rail, the old side to side jerking is gone too. 👨👧🚽🧻