Hey, i replaced my bolts on the license a few weeks ago and noticed the rusty nuts welded to the trunk lid too. It's terribly designed.
But what i found was that the bolts that the Acura dealer used was some type of a plastic screw, not a metal bolt. On mine, they broke while I was trying to remove them. Then, I couldn't remove them because they would just shear when I put the vise grips to them. I ended up drilling them out with a drill bit, using a slightly smaller diameter, then pulled the rest of the plastic out with needle nose pliers. Drilling them out was a breeze since they were plastic. I replaced with stainless, but don't remember the size. I can tell you that they are exactly the same size as the bolts on the lower retaining clips.
Hope that helps.