I'd want to try on a scrap set of barrels first, but I'll bet one could plug small screw holes in a bottom rib with a couple quick spots of MIG weld into the holes, quickly followed by a wet cloth or perhaps covering the solder joint with the heat absorbing compound sold by Brownells or Certanium. The key would be to localize the heat and contain it to a small spot and cool it before it could melt the solder. And you would sure want to hit the sides of the holes in the rib and not have the MIG wire travel through and arc on the barrels.
I am thinking this is probably how Keith Kearcher did it so reasonably as it would certainly be more expensive to remove the rib, weld and dress the plugged holes, relay the rib, and reblue.
I have also seen holes and badly damaged stocks patched over the damaged area with a thin veneer of matching walnut. After the patch is glued in place, it is dressed down and an x-acto knife or scribe is used to extend pores across the glue joint to fool the eye and hide the closely matched joint.
There was also a thread here a year or so ago that showed the work of someone quite talented who painted matching wood grain onto a walnut stock extension. It was pretty remarkable how good it looked, and it was a much larger area than a couple screw holes.
