Getting a new, factory-made extension bar (or other common and mass-manufactured piece of metal) is both
- cheaper, easier and faster (unless you happen to be pretty much away from some trading point)
- gets you a better and more reliable product (subject to caveats as well).
No matter how good welder you are, you can at most restore the instrument to its original strength that was not enough to begin with (otherwise it won't break).
Depending on your working habits and abilities, you may use the pieces to create some non-standard tool, but if you are into this, you won't ask the question in the first place.