Easy game to play with the wife.

He's tied up securely such that his hips cannot buck to wildly, and he can't block with hands legs, or by flipping over.

He's got a good lube all over his penis.

She gets him off hand, etc. job, or intercourse finished by hand and/or mouth.
As he ejaculates, she gets a firm grip at the base of his penis to do post-orgasm hypersensitivity torture on him, and starts stroking. With the other hand, she uses thumb and forefinger wrapped between his testicles and his body and other fingers wrapped around testicles with a firm grip that can easily be turned into a squeeze.

As the ejaculation ends, she strokes his penis, finishing put with a really tight squeezy stroke on the head. She simultaneously squeezes his testicles with an ever-stronger tight grip. She asks, "Head or balls?'.

If he says 'heads', she loosens the grip on the testicles to a nice just-too-firm squeeze that can be turned into a painful squeeze.

If he says, 'balls' she stops stroking the head, holding it tightly at the base to keep the blood in for further stroking. She squeezes tighter and tither on his balls until he says 'head'. Then she lightens up to a just-too-firm squeeze on the balls and goes back to a penis stroke with good solid penis head torture.

He can say 'head' or 'balls' any time he chooses for her to mix it up. She can ask 'head or balls?' and if he doesn't answer, he gets both until he does.

The game will end when his penis stops being so sensitive, her hands wear out, or she completely crushes his balls.

Tips:
-- Do not use semen for lube. It has a microgritty texture that can irritate the skin. If the penis is pointed down for ejaculation (e.g. table or sex swing), it might help keep blood in the penis longer. Also, ejaculate goes on the floor. If he's on his back, pointing his penis back to catch semen on a rubber or plastic mat on his belly with tissue on it can prevent too much ejaculate from mixing with the lubrication. She can also use a wetwipe to wipe off any semen on the tip of his penis if she is fast, throw the tissue on the floor and use the hand to quickly grab his testicles after that last spurt