I think it would be a nice gadget on a pistol, if the laser lit up when you put 1st pressure on the trigger, but on a rifle it's just fluff to go wrong. Sadly I don't know enough about airsoft pistol triggers to think of a way of doing it other than the simplest method of just creating a miniature pressure switch:
2 spade connectors, flattened, 1 with the tip folded back to form a bump, then separate them with a piece of foam, and seal the whole thing with heat shrink insulation
You could glue that neatly to the trigger, but of course it would depend on the pull weight of the trigger being sufficient so that the switch would operate before it fired.