I drilled mine out and just put a bolt through each stud. The ony other solution is to grind the head off and the rest of the stud will simply fall out. Install a new longer bolt and tack weld it to the grille support (what I should have done).

Or, if you don't have a welder, simply install a bolt retaining clip on the other side. The clip slides over the bolt & sits flush, holding the bolt in place. These are the same things holding the plastic seat spacers to the seat track studs. They're as easy as your local Home Depot.