The light is a Surfire 6P and I'm using a quick detach ring (about $5 for a pair at Bass Pro).
That was my 'temporary setup'. If you want to do something similar I'd recommend the G2 instead (lighter, cheaper, and can take more of a beating) and get the Z32 anti-shock bezel.
There was no presure switch. If I wanted to activate it momentarily I'd raise the knuckle on the hand holding the foward grip. To keep it on I could run my index finger along the talicap to rotate it on/off. The setup works ok, but if you want to do it right I'd really recommend getting a real weapon light rather than use the handheld light like I did.