Ever wonder who was responsible for creating the Nancy Drew or Hardy Boys stories? The man was Edward Stratemeyer, who also created the Rover Boys, Tom Swift, and the Bobbsey twins, all very successful.
Stratemeyer's method was to create outlines of the stories, and then farm out the writing to authors for a one-time fee. In this way he was able to generate an immense number of juvenile series books. This was the Stratemeyer Syndicate, and it was exceedingly successful.
Another notable feature of the Stratemeyer syndicate was the breeder set. Generally each juvenile series would see one new book a year, but to begin a new juvenile series, several volumes would be released up front, often three (as was done with the Hardy Boys). It seems this generated interest and drew in long-term readers.
I find this interesting from the eBook perspective, as it also seems that authors who have several eBooks available do better than those with only one. It may be worth trying: get several books ready (perhaps in a series), and release them all at once.