I have never in my life sat on a testis, but, I have given your predicament much thought & I think I have a solution.
Get yourself a fishing pole that comes in 2-3 sections. Throw out the upper section(s), they are too flimsy to handle your jewels. Attach a spinning real to the bottom (hefty) portion of the sack pole and load it with 100lb test line (don't go with clear line, could be dicey) Next you need to construct a collar/harness that is capable of holding the sack pole comfortably. Go to the store and buy a jock with an extra large sack sack.
When you plan to take a sitter slip the harness over your neck and let out enough line so that the sack sack is hanging midway between your navel and your junk. Place your sack into the sack sack & sit with 100% certainty that you will not be crushing one of your boys.