I've done this many moons ago, on a Hondo copy of a bass who's name I can't mention here. I took the neck to work, masked the existing holes off. I used a pillar drill and drilled front to back, there was some slight damage around the edges, but the lips on the new ferules hid it quite well, the back fared a little worse as the drill pushed outward, but the base plates of the new machine heads covered that.