Not sure if anyone's done this yet, but I whipped up a sight for my RTS Perceptor last night to complete his All Hail Megatron look. I used a trans-blue 1x1 LEGO brick as the base and simply trimmed it down. It simply plugs into his open eye socket and holds in very well with friction alone. As a plus, LEGO uses very solid plastic so there's no worry of it breaking. I may take a second stab at it since this was a little on the quick and dirty side. Sorry for the crappy phone pic, but it's all I have to take photos with right now.