No offense taken Scott, it's a light(helium)-hearted topic…
I’ve got some ribbing from some SoCal members (who having a birthday party?) but in the end they thought it was kool too. One guy even told about balloons being used in Lechuguilla
but a websearch shows it done in Carlsbad Cavern:
1982 In October, Cave Specialist Ron Kerbo and Geologist Mike Queen use light cord, balsa wood, and helium balloons to float cord to area 200’ above Baby Hippo area, snagging a stalagmite. Later, both climb rope into area later named Balloon Ballroom. -
NPS Source
Anyway, we did learn a few mods we need to try for the next time: use light sewing thread (the string that they use for balloons is too heavy), use mylar balloons (rubbers are too permeable).

BTW, we tied marking tape every meter from the top of the balloon(s) and yes, we added another because after a while one could get it up!

(Edited to reflect balloons were used in Carlsbad Cavern, not Lechuguilla - pub)