I used to have a full lexan windscreen for my BMW, I could nto have simply cut it out because it had bent ridges for reinforcement. It was securely velcroed so blowing out was not a problem. I think that if something were to be done to keep the windscreen in for a boxster it would have to be either taped in, velcroed, or my favorite... designed to have been pushed in from the front and not the rear.
And im not putting those things on my car so someone else volunteer, lol. Oh ya, I know of a cheaper and less conspicous way to get the same effect as those lexan pieces.... Its called saran wrap. If you just cut some saran wrap to shape and put it in the inside of the windscreen with maybe a little adhesive around the edges youd fill all the holes for free and you can just rip it out if you dont want it anymore.