another variant on the first idea- the "girl on squirting sybian inside a vat that gets filled with gunge".
Have two girls go at it, maybe a teacher introducing a student to the world of 'gunge fucking' after she's caught sniffing the teacher's jacket/scarf while masturbating in a closet. The girl is shy at first, until the teacher mentions her special reward- afterwards, they'll 69.
Cue the same vat, only with a sybian designed for two- four vibes, one for each girl's ass and pussy. The way the vibes are positioned, the teacher is sitting behind the girl, so she can rub the student's breasts, lick her neck, and tell her how good it's going to feel when it comes. The scene progresses, with the teacher instructing the student to tell her how it feels as she rubs the gunge- preferably chocolate- on the girls breats and shampoos her hair with it. The student tells her- and the audience- how wonderful the vibes feel, then gasps when both she and the teacher are treated to nice, warm loads of lube-slime in their asses and sugarless vanilla pudding in their pussies. As promised, they 69 after being cummed in several more times, but then the teacher playfully declares that such a slutty student deserves a special punishment, and makes her ride the sybian again, taking as much pudding as she can tolerate. Then she finishes her student off by making her sit on a larger anal vibe, eating her out while the vibe oozes thicker slime in her ass. Then, to end it all, the girl is made to take even more pudding in her pussy, made to come it out into a pie pan. The teacher writes 'A+' on the pie in whipped cream and then slowly presses it into the smiling girls face as the student is given one last blast of lube-slime in her asshole. The pan is removed to show the naked girl moaning and licking the pudding and cum pie off her face. Video ends with both of them exposing their oozing, cum filled assholes to the camera.
A guy can dream, can't he?