With my hands I have found that weighing is much, much easier. So far all of my flavors have dropper tops, if not I have a lot of small bottles I can transfer them into. I've had to do that on a couple where the adult-resistant caps worked a little too well.
I have my 100 mg nic in 125 ml bottles and I use one of those at a time to make up a batch of base just a little stronger than the highest nic level I want, and keep that base in ketchup type squeeze bottles. I use Hotrod's JuiceCalculator which has the correct weight adjustments for PG and VG, and mix right into the bottles.
Put bottle on scale, tare to 0, add correct amount of base and pg or vg to bring to an exact nic level if you want to be precise, tare to 0, drop in flavors, taring after each one, put the caps back on and you're done - except maybe wiping a couple of drops off of the scale.
Everything that I need for a set of juice making: