Hmmm.. good idea!
I re-use the 2.0 bottles with 1.7 but it's usually to fill with hydrated 1.7 from the pitcher (in order to mix a new batch to sit in the fridge for enough time.) Just adding the powder and mixing on the spot would be convenient for on the go.. Getting the powder in the narrow bottle opening sounds challenging though.
I wouldn't worry too much about exact measurements.. just eyeball it.. Personally I probably have a 5-8% variance on the water:1.7 ratio even when I mix in the pitcher. When I make Schmilk it's probably more like 15% variance milk:schmilk. It all evens out over time and makes the process that much easier.