The Surefires/Rogers technique is when the shooter grasps the flashlight in between his "pointer finger" and middle finger, like smoking a cigar, in his off hand. THen he attempts to use that hand as support for his dominant hand firing the gun, like a normal two handed firing grip. The flaslight must have a momentary switch on the butt, which you use your offhand palm to activate.
I hope you can understand my chicken scratch
Edit: I find the Harries technique to be faster, with a stronger grip on the light. However, the Surefire/Rogers technique has its merit, especially when shooting around cover. Also, I find that the SF technique is easy when using my Z2, but when trying it with a friends 6p, I dropped it during recoil due to the lack of grip ring