Barrel too short? Last I knew, from an FFL gunsmith, if you have an extension silver soldiered on, that is permanent for barrel length. So if you cut too short, you could add on a bit... and be legal.
No doubt, filling can be done, but at what cost? I doubt it would be cheap if it were any good. I have seen welders that did amazing things. Of course, if you drill out the inside, oversized... As suggested, a sleeve could be fitted over the outside. Good man with a lath, turn down the barrel a bit and you would never notice it... Again, cost. If you really cannot live with it (and earplugs) then talk to the machine tool men and weigh their price against a new barrel. I would be inclined to invest in a quality barrel and maybe a bit more length. luck.