Try "battery snap" from the Market.
It's a battery widget which displays (via a handful of different little graphics, you pick) battery life by percentage and time remaining.
The beauty part is, if you click the widget, you can view stats and graphs that break your battery usage down not by app, but at least by time frame - there are preset timeframes as well as a dynamic viewer which allows you to drag timeframe in or out just about as close as you could want to get.
I doubt it does exactly what you want, but it's certainly the best battery widget I've found thus far.