To split hairs, my suggestion does not technically meet UL listing, even though it can be done with off the shelf components. The "3 prong to 2 prong" adapters are designed to have the ground pin connected to a ground-not that I have ever seen one used properly....
Not sure if "off the shelf" adds any liability protection-I also understand the desirability of the stinger cap from a noise standpoint.
I may be the only person who ever tried to use a 3 prong adapter properly, until I realized that the screw on my outlet faceplate wasn't grounded to anything so why bother?
For back-line use the ground lift adapter in combination with a GFCI power drop actually could protect a musician from a hot mic finding ground via that power drop EGC.
Johnny the engineer likes the GFCI stinger cap very much
, Johnny the businessman doesn't like modifying UL listed gear casually.
The win-win is to get this blessed by UL... In an ideal world they should, but some business will need to pony up some cash... I suggested it to one GFCI maker and the last time I called the engineer there he didn't take my call.
but I haven't given up yet.
JR