Simple version. Multiply the amount of vinegar by 0.0357 to get the extra amount of lye necessary.
If you are adding your lye to your vinegar add it with caution. Also do not let it sit for hrs before using because the lye and vinegar will react and form sodium acetate and will get pretty thick, although it can be soaped with, but I prefer to use it before it thickens. Actually I use 5o% vinegar in my batches because I like to masterbatch my NaOH, and they are hard enough, but then again my recipes are already hard soaps. I use powdered milks if making milk soaps.