Have these so-called pilots ever been told that balloons need not be roundish, like weather balloons or birthday balloons? A 3d box-shaped balloon where the only supports are plastic, helium or hydrogen filled cross-members and open sides, could easily be constructed and launched into the high altitude wind stream.
Somewhere in a box I have photographs of different shaped hot air balloons from a balloon race I was in some 25+ years ago. IIRC, one was of a truck (FedEx? USPS?) a birthday cake w/candle, prolly some others as well.