how does this work? I wqould be interested also. I party pig half my batch and bottle the rest. Right now I use a Priming Sugar spreadsheet (found somewhere on HBT) that calculates your amount of sugar to add to bottling bucket based on your desired CO2 level.
My only drawbacks are 1) you have to estimate the amount of beer being bottled based off the lines on your bucket/carboy 2) carb level can vary based on ambient temperature, at least from what I have read.