I use a kit that connects to the front tow hook location, for times when I need a front plate, inspection, etc.. *edit - just like the one below.
They are required here in Mass as well. No need to add more holes in the bumper. I found this was a quick solution that I could take on / off easily and also store it securely in the front trunk. If you get pulled over you can always ask if you can put it back on, maybe you'll get lucky...
http://www.moweraxle.com/licenseplatebrackets/porschetowhookkits.html
There are a few other types of tow hook plate kits, if you are good with metal work you could prob. even make something to fit your needs.