The 1/4x20 insert would work. Maybe a bit of threaded rod, adjustable coupler and a flange. I would NOT use sticky tape or the "super-grip" pads alone. If you center the weight on the bracket and it's level, the speaker will sit there. It's just top-heavy and anything less than solid attachment would make me very nervous.

Also, probably obvious but stud-mounting is required. Don't even think about using the drywall anchors from the kit.