I think that the inserts are sort of crimped in place from the factory. Mine did not look to be welded. If you have an air ratchet, get the bolt started and then run it up with the air ratchet. The higher speed will cause it to catch and run up tight.
I took mine to the dealer for the 20 hour service and bitched about this since I couldn't install my new aluminum skidplates.
They agreed it was a warranty repair and called Kawasaki. Several hours later the technician called back and said to run a nut on the bolt and tighten the nut against the frame. Then tighten the bolt and this will expand the flair insert and restore it's holding abilities. Seemed relatively successful but I still have a few that turn when I installed my new skidplates. I'll make the dealer deal with it again on my 50 hour service.
Of course this only applies after you get the lil' bastards out. As previously suggested, the dealer used high air pressure to spin 'em out.
I use my fingers to get it started and then an open ended wrench to wedge the nut against the frame till the nut seems to pull it. Its a pain but it works. I have replaced some of the broken welded tab nuts with locking bolts on my Brute Force. It has the same issue.