The trick to successful drilling is to use a milling machine.
The problem with welding a nut on is that although it often works, if the threads are galled it is 100% guaranteed that it won't. And then you've hardened the end of the bolt you now need to drill out anyways.
The best is when someone drills, breaks an EZ OUT, welds a nut over that, breaks the nut off, and then gives up and brings it to me....