If you have access and can reach the back of the holes you can use a piece of copper on the back side and plug weld em from the front. the weld wont stick to the copper. You can by some fancy copper tools for this but you can also achive the same by going to the hardare and buying a small sheet of copper and a big magnet.
Here's some of the tools
http://eastwood.resultspage.com/sear...ustom&w=copper