I'm guessing his "punishment" material has run out? Eventually we all run out of ideas as our muse flies the coup.
I guess I'll throw in a few ideas:
Have him watch his favorite TV show/movie while she is bent on all fours before him. Collared of course. Have him rub his hands underneath her and really make her soaking wet. But make sure to throw in a few good spankings whenever a code word is said. Something the show or movie is famous for saying multiple times. Do not allow her to cum at all. Once the TV show is over, do not succumb to her desperate pleas. Just do whatever else you want.
Another thing to try is to have her tied up and in nothing but a smooth pair of panties. Put on a thin layer of whipped cream on her back and on her ass cheeks. Lick off a little with your tongue and then spank that area. Lick off a new area and reach underneath her and squeeze her breasts nice and hard. Work the nipple back and forth a bit with your middle finger. Next reach back and spank the new open area. Continue to balance pleasure with pain. It could be spanking, twisting the nipple a bit, pinching the butt, scratching lightly and I mean lightly down the back of her thighs. It will drive her wild and yet should slowly increase both the pain and pleasure. Finish off with grasping the back of the neck with one hand and spanking the hell out of her, or roughly squeezing tugging and pulling her breasts.
An interesting one to try is to dip her erect nipples into a bowl of warm milk. Keep them submerged while you stroke her kitty. When you feel the time is right. Lay her down and suck gently on the milk covered nipples then increase the suction. Once the suction has reached its maximum possible amount, run a flower or something soft between her thighs. Out of nowhere bite the place where the flower touched. Don't draw blood obviously. Enough to let her know that those were teeth. Lick that area quickly, then bite a new area. End the session with with you placing your mouth directly onto her kitty and growl into the hole. Make sure your lips are buzzing as you do this. Once she starts to squirm and shout out with pleasure simply get up and tell her to do something else. The key is to leave her wanting more. To crave the finish. Also each bite will leave a mark for a few days which will remind her of what happened.
These are all more playful punishments. If he needs something truly painful then try giving her a wedgie while paddling her ass hard. Or stepping on her kitty and pinching the clit with your toes.
Use your imagination. There's always a new punishment.