Hi Roudy,
Yes, I've done trigger stops on the plastic trigger guards. It was quite simple...
I selected a stainless allen drive set screw of appropriate dimension (I use 8-32's or 6-32's)
I then drilled the back of the guard the approximate diameter of the screw minus the threads,
Drove the screw into the drilled hole "tapping" the plastic with the stainless screw... heating the screw a little helps create nice form fitted threads in the plastic.
Last, trim the screw to desired length if neccessary (enough on the working end to serve as a stop leaving the driving end flush or just under with the rear of the trigger guard so it doesn't gouge you in the middle finger when the rifle is fired)
Clean off any plastic 'slag'.
:x HERE'S THE RUB!
Pulling back the hammer to full cock induces a rearward movement of the trigger past center, that is sear engagement. If you adjust your stop screw to just allow letoff, you can't re-cock the action because the take up is preventing that rearward overtravel required to achieve sear engagement!
Adjusting to prevent this results in a lessened but not ideally crisp amount of trigger overtravel.
I'm not sure how this could be tuned out without causing an 'unsafe' condition of less than rigid sear lockup with the hammer back.
Steve