If I understand your dilema then that recipe calculator won't help you because it only uses one positive nicotine mg componant and 3 possible 0mg componants (water, pv/vg, and flavoring).
OK, you have some 12mg juice that you want to bump to 14, 16, etc and you have some 100 mg juice in order to accomplish it.
The following ratios will yield the following results (by volume)
12mg juice /100mg nic /final mg juice
100 parts to 1 ====12.87mg
100 parts to 2 ====13.72mg
100 parts to 3 ====14.56mg
100 parts to 4 ====15.38mg
100 parts to 5 ====16.19mg
100 parts to 6 ====16.98mg
100 parts to 7 ====17.75mg
100 parts to 8 ====18.51mg
100 parts to 9 ====19.26mg
100 parts to 10 === 20mg
(Editor won't let me keep my column format, let me know if this doesn't make sense)
If you look closely, this is not a linear shift. It was easier for me to do it than to explain it but I think I covered the range that you wanted. Concidering that 20 drops is roughly 1mil, then you could easily adjust a 5mil bottle (roughly 100 drops) and add the number of drops from the second column to get the resulting mg that you need.
Hint your 10 mil bottle of 100mg nic will go a long way.
Hope that helps
eHuman