Not having a suitable drill press is one hurdle...

But I had the thought - of first once I have the bridge position set then clearing the bridge side hole areas of denim, then drilling 1.5mm holes through to the other side essentially to mark the positions on the back, then clearing the denim on the back for the ferrules and then drilling the full sized holes. The thinking being that initially using a 1.5mm drill should remain straight enough through the body to maintain even spacing and would be least likely to tear very much at the denim.