kiplynx, I think you are indeed wrong :/ I did the illustrations, and I know I've got a handle on what the exercise is. I'll attempt a simple explanation.
The Mandingo Stretch, right handed, half twisted:
The initial grip is palm down, with your thumb facing your body.
Without letting go, bring your hand up and around the right side of your penis (if you're using right hand) and place your pinky on your pubic bone.
Now you are in position, your knuckles should be resting on the dorsal/top side of your penis. From here you can push down or pull out to generate force. Use your pubic bone as leverage.
Note: This is the bundled version, to do the unbundled version, begin your grip with a twist in your penis. This is because the action of bringing your hand up and around your penis will naturally create a half-twist.