Not really a trick to it. They go in from the back, unlike other glasses. Put the top of the lens in first, and then align the 'teeth' of the lens with the 'bump' on the bottom and push the bottom over the lil 'bump'. Voila!
Getting the other lenses out, is a pain and you have 2 options:
#1. screw up the frame while trying to save the lenses
or
#2. screw up the lens while trying to save the frame from damage
There is no good way to cut the Switch lenses after you have taken the old ones out...so either use the 'outline' that is floating around, or trial and error until they fit...