I realize this is a necro-post, but in case anyone comes by to see it. I used a basic Milwaukee rotary tool. (Also known as a Dremel!) with the included cutting disks and it worked great. Neat lines if you plan it out ahead. Beware that you will generate a lot of plastic debris so wear safety glasses, but it went smoothly and only took a few minutes to cut both vents. Used the broad surface to smooth out the edges as well.