In addition to doing the above with the jig saw and router, you will need a template guide to keep the router from removing more than the desired hole, and a top bearing compression style flush trim router bit. Because it's very hard and both surfaces need to be as chip free a cut as possible, one of the compound cut flush trim bits that have both up and down shear blades would be a good idea for this. Yes, they are expensive. Don't expect to cut very many (more than about 10) of these without replacing the saw blade as well as the router bit or at least getting them re-sharpened somewhere. Buy good quality, like Freud, CMT, or Whiteside bits.