I have an Olight Warrior in an offset mount on my 6920. Its mounted to a quad rail and has a pressure switch to activate it (pictures below). I'm not using a verticle fore grip though but I am using a Magpul AFG.
How is everyone mounting your pressure switches without the use of a verticle fore grip with the switch pocket?

I use a Magpul AFG and a tape switch. I have the switch mounted on my rails at the 10-11 o'clock position. It is in between the top rail and the left rail. I used velcro after cleaning with alcohol (Not Beer). This works great, will not come loose and is easily reached and pressed. I have Troy rails.
Tango down pressure pad panel and LaRue index clips

^
This
Velcro is handy as well
Velcro it to the mag well.

I absolutely HATE Velcro/glue mounted pressure switches/pads! For my M951, I use a
Surefire SR07 Rail Mounted Pressure Switch...no chance of the Velcro/glue to wear or
come off at the worst possible time. IMO...Velcro or glue have no place on a firearm.

I use a bicycle tire inner tube, stretch it around the forgrip. That shit won't come off by accident.
I don't know what kind of rail you're using, but I was able to slide a Surefire tape switch in between the ledge of the AFG and the light on the right side rai on my VLTOR CASV, it was in there pretty good and in just the right place for my fingers to activate it. The length of the wire on the tape switch was short enough that you couldn't really slide it out without removing the AFG or the light.
I use a velcro cable-tie to hold it in place. It holds well, and can be taken off easily if needed, with no damage to the firearm.