This stretch rocks! I've included it in my routine & I'm really feelin' good about it. To me, it's "the" stretch to do to feel what a good stretch is supposed to feel like. Thanks again Still! Wish me luck!
I've done something similar as well. I would pull more to the side, using only one hand just like your right hand in the pic - pulling my dick against the underside of my leg, would be your right leg in the pic. After stretching as hard as I can with the one hand, I'd hold it against the leg and move my leg back, the leg muscles increasing the stretch . Imagine your second pic above, without your left hand gripping, and as if you were to do a back kick with your right leg while holding the grip. Your dick and gripping hand make a sort of "loop" that your leg pushes agains.
Also, as well as moving your leg you can just straighen your upper body to apply more force. I seem to be able to hold this leg-assisted stretch longer than hands alone, as well as get more force. You can use your other hand to brace the grip, just have to reach over the side instead of between your legs.
This is something that is good to try with all manual stretches . It is amazing how slight body adjustments can create a new fulcrum point and with manual stretching this fulcrum point can make all the difference in the world.