If you mean premix the dry salts and store them dry, to be dosed dry, that can be a problem if you aren't able to mix them well. It would be about 4 parts KNO3 and 1 part KH2PO4, but unless well mixed, and unless the particle sizes were about the same, the mixture might not be homogeneous.
To clarify, i want to mix my weeks dose for each of the 3 days ( Mon, Wed. Fri - 1/2 tsp. KNO3+3/16 tsp. KH2PO4+ 1/4 tsp. K2SO4 combined in 1 container,so i would have 3 containers with the NPK for each of the 3 days) this would make it easier fo just dose 1 container in the morning before i leave for work instead of measuring each salt .