Here is how I put a Kroll in my G2:
1 Remove the bezel and take the batteries out.
2 Remove the switch mech from the tail cap. Leave the rubber boot in place.
3 Remove the rubber boot from the Kroll.
4 Wrap enough alimumin(sp) foil around the threads on the Kroll so that the Kroll fits snugly into the battery tube.
5 Screw the end cap onto the battery tube.
6 Put the batteries back in and screw the bezel back on.
7. The Kroll shoul now work normally.
8. REMEMBER...Batteries should go in via the bezel! I f you use the switch end to replace the batteries, you could loose the switch!