The goal here is to raise the gravity by .003.
Final Volume * (1 / ((OG - FG) / .003))
Example:
5 gallons * (1 / ((1.071 - 1.017) / .003)) = .27777 gallons
Convert that
here to 35.55456 Ounces.
Throw this in the freezer until bottling. Then thaw it out, heat it to 180 to pasterize, cool it and pitch it in.