I've never encounterd a factory dual setup, so I have no clue as to how they hang. If it's a traditional aftermarket set up, it's held in place with a self tapping bolt, without a nut. The problem with a nutclip arrangemnt is that there is no way to access the area to install one.

One solution would be an oversize self threaded bolt. If you cannot find an oversized bolt, you can take a machiene thread bolt, saw down through the center of the threaded area, then crush the opening shut. This will provide a tapered end, allowing you to wallow the bolt in the hole.

Yet another option is a threaded insert. One version of a threaded insert is installed in the same fasion as a pop rivet. Kinda' like a helicoil, except that it's crushed in the hole like a pop rivet.

Another version crushes in the hole, but it has a specail tool that holds it in place, and a bolt is ran through the threaded area and drawn up, crushing the instert into the hole.