Why not simply indoctrinate a god similar to Nietzsche's?
A better question is, why indoctrinate people at all in something that isn't true?
Well, the kind of god he was talking about isn't a personified entity that looks and talks like a person. It's just the embodiment of various forces of the universe, luck, and some aspects of the human psyche. No one will actually believe an actual god exists under that concept. For instance, if I were to say "God willing", it would just mean, "if I'm lucky". Now, the aforementioned concepts that this kind of god would embody do exist, so it isn't really false or true. It's a symbol.
The concept of music doesn't really exist anywhere but our minds, in reality it's just a sequence of sounds with no objective meaning. That doesn't mean it isn't a valuable part of a culture. There needs to be a way for a particular society or community to encapsulate it's beliefs and values and propagate them. I know you don't like the concept of god because of it's historical use... just say "the universe" instead. It doesn't really matter what we call it, so long as it is communicated to people.
I know you said people need to grow up, but it's not the individuals this is done for. Many, or even most individuals don't need this system in place. But a group of people does. Communicating with large groups of people is tedious and requires simplicity. Psychologically, groups of people become much, much less than the some of their parts as the number of them grows.