Just mix in drops instead of ml. So, for a batch that is say;
3 ml of VG
1ml of flavoring
3ml of nic base
3ml of PG
in drops would be;
3 drops of VG
1 drop of flavoring
3 drops of nic base
3 drops of PG.
That's like a microbatch, but you can always just redouble it to get the desired quantity. For approximately 1ml of juice, that would be times 3 for;
9 drops of VG
3 drops of flavoring
9 drops of nic base
9 drops of PG
Of course, you have some variance in drops per ml for different fluids, but you don't have to get it exact to get a good idea on the flavor concentration. You can just leave out the nic base if you want anyway. Probably a good idea just for flavor testing. I can't tell you how many times I've overdone it on the nic trying different flavors. I just do it without the nic anymore.
Alternately, you can simply use your mixing calculator to provide quantities in drops rather than ml. In that case, you can actually calibrate drops per ml for the different fluids and get more exact numbers. I don't use a mixing calculator at all anymore so I have little tricks on how I do that stuff in my head with the aid of a regular calculator. The above is how I switch between drops and ml.
You can calibrate your drippers and fluids by measuring the quantities into a syringe with the plunger pulled if you don't have a 10ml graduated cylinder. Measure the drops per ml for the fluid and dripper bottle then input the quantities into the mixing calculator.