Even a high strength Nic will be mostly VG or PG depending on what you order. For instance, 100mg - 100% VG will be 10% nicotine and 90% VG. The only way around this is to use PURE nicotine which is usually 99.9% (990mg) pure. I personally would not touch the stuff being that it is very dangerous/poisonous
If I was to mix with Nic 100mg - 100% VG in the calculator I would set my target PG/VG ratio to the highest VG % allowable and use flavoring w/ a VG base. Instead of adding the pure VG to your mix, use your cut down 20% water VG. Don't use the box for water/vodka/pga.
When using a PG base flavoring, your PG/VG ratio needs to be adjusted to allow for the PG of the flavoring.