I went for a slightly different method using a screw inserted the other way around, and some nuts to hold the switch in the right position, i've posted some snaps in case it would be useful to other modders out there:
I drilled a hole for the screw, and a shallow larger hole over the top, to sink the screw head slightly below the surface:
Then on the other side, I threw on 2 nuts which provide enough height for the switch to sit up on and stay in line with the trigger (the amount of nuts you need to use will depend on their size, in my case, 2 provided the correct height):
Then add the switch, just like on skate323k137's photo the back of the switch will be supported by the plastic casing. In the following photo there is only 1 nut fastening the switch to the screw, later on I added a second one, just as a safety measure to stop the nuts from rolling off if they get loose, I guess instead of that you could even drop some glue over the nut and switch.
At a later point i might even drop a dab of blue paint over the screwhead, just for prettiness' sake
Also, take care when tightening the nuts, you don't wanna tear the thread on the screw, but you also don't wanna have 'em loose enough to start rolling apart when you're mowing down the magician from HotD.
Now time to destroy some henchmen and zombies! Thanks again skate323k137, legend!
