Jeff,
re: "The problem, which I have yet to overcome, is how to cut out the key holes so it does not look like crap."
Try your local craft (Michael's or JoAnn's) or leather shop and look for a punch which matches the size and shape of the hole you need to make. If nothing found, and it's real important, a local tool and die maker ought to be able to make you a punch (essentially a cupped (concave) end of a piece of metal with a sharp rim). I needed a round punch like this once upon a time, about 3/16" in diameter, and my Dad machined one for me. Took him longer to chuck it up than to actually cut it!
Use it by placing your plastic sheet on a relatively firm surface you don't care about (scrap wood or tablet backs work fine), put the punch where you want a hole, and hit it with a hammer. (Helps reduce stress and anxiety, too!) Practice first on some spare material, to get the feel for the right amount of whack.