That's more or less what I'm doing with my current revision project -- going back and inventing extra scenes, most of them taking place before the story ever starts, to get a better handle on the characters. But I'm prone to RSI, so I generally don't type those things out; I only imagine them in my head. Which means I don't get down to the level of sentences and dialogue, for the most part. It develops character just fine, but not voice.

It's all the more frustrating because I know one of the major problems I need to solve with this revision is the beginning, and one of the flaws of the beginning is the lack of a distinctive voice. But I haven't yet been able to make it pull together.