Pain in the ass, it what you have.
Measuring out 5mg or 10mg of the powder will drive you crazy.
I would measure out several and get a feel for it, then eyeball the rest. I did this with 50mg (oxy) and that is a very small amount.
I found a child's kitchen playset spoon that worked perfectly for the amount I needed, so the eyeballing was pretty accurate, but not precise.
The other way would be to put the measured var powder in the cap, then fill the remaing space of the cap with say cornstarch...now measure the total powder, subtract the var powder now you have the amount of "filler" you need per cap...let's say you are going to fill 50 caps (which happens to be the # you can do with the capmquik) multiply the filler amt x 50 and var powder amt x 50 and very throroughly mix the two...then you can pour the powder/filler onto the cap deck and simply fill the caps. This is obviously not a liquid solution, so the amount of var to filler from cap to cap will vary, that is where the mixing thoroughly reduces the problem.
Makes sense?
Good luck.
Rugger