A choice that takes you back to the start with the new paths open would be the way to do this, I think. Sort of a New Game +, not actually just ending the game and having the reader start it up and go through it again. Even if it was just a matter of being able to make more informed choices with info they didn't have before, it'd be difficult to structure the story so they weren't stumbling into what was supposed to be the later content without some way to track what they've seen so far and gate other parts off accordingly.