Sit on his face

You straddle his face, completely covering it with your full ass. He mumbles a bit beneath you. He doesn't seem to grasp his role in this arrangement, so you grind your pussy against his mouth and face. He sputters and coughs a bit but finally begins his own stimulation.

His oral work is passionless and inept. He mulls your labia in his lips between prods of his tongue into the entrance of your vagina (and on more than one occasion, your urethra). You slide back a bit, forcing him onto your clit. It's more pleasant, but he is far from amazing. You don't really care much. You love listening to his grunts and gasps, twiddling your nipples in self satisfaction between teasing flicks of his cock.

Unfortunately that cock isn't holding up to your ****. His erection flags and despite some more earnest manual work from yourself, it is gone. It's clear he is having trouble fulfilling his job requirements.

It hardly seems worth the effort to continue but maybe you can do something for him. You have the time.