I will pass along what Greg suggested to me months ago...
Get an old syringe and draw up some sort of liquid (something like milk is good since you can see the unit lines clearly) to a full unit line. Rather than pushing the plunger on the syringe, twist it (kind of like twisting a knob) and count the drops that make up 1/2 unit. I would try this a couple of times for the sake of consistency. Then, you can use the number of drops as a means of approximating these doses.