From a relatively new builder's perspective, I've tried that method to intially cone the outer hub from a stock BSA wheel, with little to no success. I would either use the wheel as the the NDFW or chuck it in the trash.
John is having a sale; I would take advantage of it...
I chuck up a 1" q tip stalk to be used for a mandrel and sand it so the bore is a snug fit. When the wheel is spinning true, I use a piece of 2000 grit on up to 12k and Johns polish. The paper can be folded just right to get in there and hug the existing contour of the hub. Use your finger as a backing and sand very lightly. The distance(center of bore to the nic) is so small that it is very forgiving and it doesn't come out distorted when done right. I have done this before with success and it's better than scrapping the wheel. If the nic isn't too deep, it should be no problem sanding and polishing it out while still maintaining the original trueness and integrity of the wheel.
A nick will most likely be an innie and an outie. The plastic gets dented and the plastic from the dent has to go somewhere. This may not be true in all cases but most nicks have had an impact with something.