I would definitely not drill bars not designed for internal routing. You'll create a flaw that stress can concentrate in, and if it breaks you're going to impale yourself on jagged aluminum tubing at speed, which would suck.
Those may not fit in flop and chopped bars, depending on the inside of the bar and exactly where you cut. They wouldn't fit in mine. You can take off the shim, if you don't need it. If those brakes don't have a cable exit allowing you to "aero" route the cables under the wrap, then I'm afraid you're not going to be able to use them. You could save them until you've picked up some purpose-made bullhorns- personally, I don't like the way those are shaped much, so I've stuck with clamp on levers.