One of the cheapest ways to do this is to buy a Kroll switch for a Mini Mag light (costs about $5.00). When you get it, take the rubber tailcap off of the Kroll, wrap the switch up in aluminum foil, and replace the G2 switch with the Kroll switch, keeping the rubber switch cover for the G2. I have this setup in my own G2, to which I just installed a DX Q5 drop in. Works fine, but the switch does fall out when changing batteries.
There were some threads on the specific procedure for this along with pictures, but I don't have the link for it.
BTW, this will make it a forward clicky.
BTW2, this works with the old, incandescent/xenon G2; do not know if it works with the G2L ...