When bottle conditioning, you don't need to know how much sugar is left in the beer to calculate priming sugar additions. The reason you take gravity readings is to make sure the yeast have chewed through all of the fementable sugars before you add more sugar to prime. Also, the reason you care about the fermentation temp isn't related to residual sugars in the beer. You care because colder fermentation temps result in greater levels of CO2 being dissolved in the beer. You add less priming sugars to lagers because of dissolved CO2, not because they have more residual sugars.
But, you are correct. A good place to start trying to find priming rates using CO2 is to use a volumes chart.