Another suggestion would be to cut a template of the corner radius and then, with a scrap of the base in hand, head off to a custom woodworking shop (or friend with a lathe ) and have them make round corners in the profile needed. The center would then be drilled to provide the inner radius, then the piece would be quartered or cut into thirds, then custom fit/cut in place.

Another cheaper and easier solution would be to leave the base where it is and just return it to the wall instead of having the blunt cut that now exists. This would require removing the section from the wall to make and fit the cuts.