Aerial bombing was used in 1943, I believe it was a 250kg time delayed bomb. Obviously dive bombing a "formation" is harder then it sounds; the idea really was to break up the formations.
Not sure how wide spread it was; I tried to do some research on it but really couldn't find anything more then a field modification. Far as I know it was only Fw-190s that used them, the drag was considerable - the bomb shackle would be stuck on the aircraft making it ultimately useless as a dogfighter even after the bomb was dropped.