At the point of no return, quickly bury your face in to the right shoulder of your woman and, for the love of god, do NOT resurface until you're 100% sure you've regained full control of your facial muscles. To ensure you get the full 'clamped on' effect, therefore completely eliminating all chance of her wrestling your head free and witnessing your best Stephen Hawking impression, it may be desirable to hook your left arm carefully but firmly around the back of her neck while securing her left leg around your midsection tightly with the right arm.
Guy A: "My girlfriend loves when I crack out the shoulder bury because she thinks I'm trying to make an already seriously sensuous moment even more intimate."
Guy B: "WIN!"
Guy A: "Yes. But little does she know I'm simply ashamed of my jizz-face."
Guy A: "Is demonstrating the shoulder bury on my male friend, in someone else's house, on their bed, in front of some people I've only just met, okay?"
Guy B: "Not really."
Guy A: "Well, I did. And all those men present that were previously unaware of the technique WILL thank me one day."