I wonder if it might be easier to do the serial dilution of the ascorbic acid in water. It should be much easier to thoroughly mix than flour. If you're adding water to the mixture anyway, you can replace some or all of it with the diluted ascorbic acid.

My bread-making is much more primitive, but if i add salt and sugar, i do it by dissolving them in the water, to make sure they're evenly spread throughout the dough.