I agree with John and the others. It's not an unheard of technique, it's one that does require specific training by a qualified instructor. I've had training in it and am still training in it. (To me a person can never get enough training).
I actually made a veiled reference to it in a reply I posted about a month ago on a thread:
I always think in the terms of you never know when you might need to be using an arm or hand for deflection or close combat while using your other one to make a quick draw and get your shot off. Hence why I prefer my crossbreed IWB in a combat cut, carried on the backside of my hip area. I can draw with a clean sweep and not have to worry about snatching clothes up (and I will admit, surgically enhanced female parts, like trying to appendix carry.) That leaves my other hand/arm free to throw up a block, etc.