If there were to be a prologue similar to The Dark Knight, it would have to be Bane breaking out of prison. Simple as that. This way, we not only see the intelligence of Bane (as prison breaking is obviously a difficult task), but also his sheer strength and energy.
However, what I would do is this:
A young Bruce is falling down the well into the cave. Same scene from Batman Begins, the bats are flying around him and he is scared. But off in the distance, he sees a humanoid-bat figure. It turns into a bat and flies away.
If you make yourself more than just a man, if you devote yourself to an ideal, you become something else entirely.
Bruce training scenes quickly cut, we see the progression of Bruce. Bruce returns to the bat cave. This time, he endures the swarm of bats. Same scene from Batman Begins. But off in the distance, he sees himself as a child, kneeling over his parents. He is the human bat in the distance.
Which is?
A legend, Mr Wayne.
Bruce wakes up, similar to the way he awakes in Batman Begins. This time, however, he is in the bat cave.
If Nolan started the movie similar to that, I would squeal. Like a girl.