I got away with using some washers and vise grips when I did 3 of them for my wife's ZJ. Put a bunch of washers on the bolt and thread it into the nutsert. Stick it in the hole and then put some vise grips on the nutsert (and washers that it grabs - so they need to have the same outside diameter) as TIGHT as you can. Then tighten it down until the nutsert is grabbing the body and not spinning. The remove all the washers and tighten down completely. Kind of a PAIN.
I just bought some more from a local fastener shop, they suggested to put a nut on the bolt, screw the bolt into the nutsert, then tighten the nut against the nutsert while holding the bolt still. I haven't tried that yet, but it may just unthread the nutsert and not work. It's worth a try.
If those don't work, I'd find someone to tack weld it before I'd buy the tool.