I don't think I've ever seen this done: the guy cums in her pussy, and as soon as he's done cumming he immediately pulls out and shoves it right up her ass and keeps fucking her from the same position, the pounding rhythm serving to make the cum drool out of her pussy even better. This would probably be best in doggy, but also would work in missionary -- it would be HOT in reverse cowgirl if the girl does the work. This would be MUCH better than the usual stop-everything-and-wait-for-the-cum ending to creampie scenes.