Amazingly quick learner!
I was at a major venue this weekend. With little to do while waiting for the event to start I was killing time by inspecting their wiring. Most of it appeared to me messenger supported with the bare supporting strand used as the neutral, so no EGC run with the feeders (A disconnect was labeled clearly defining each conductor). However, the disconnect was mounted to the steel structure-which in this particular case also clearly served as a grounding electrode do to foundation bolts-it was attached through beam clamps as in this picture. If this passed an inspection,one would assume that these beam clamps would be acceptable for grounding. Much cheaper than weld clamps and the ones I like have two 1/4-20 tapped holes-perfect for attaching lugs to connect #12-# however big you need to go (within reason-I have used 500 mcm grounds before-but that is not common and would be a fairly large sound system). In any case, they would clamp securely to any angle or structural members on a stage-I get them for about a buck a piece.