Yep, I cut mine (removed the button covers).
You're gonna need a ridiculously sharp knife, preferably a scalpel, and very small scissors.
I'll tell you this: cutting through the leather is cake but the plastic under it is a bit of a PITA, and keep in mind that I was cutting from the edge. If you're basically making a hole in the side of the case, it won't be easy. For that, maybe use a pin or something to poke holes in the shape of your cutout?
But yeah overall I don't recommend it. The case will look pretty bad when you cut into it, guaranteed. The edges will be rough and bad-looking.