I am not a fan of doing it this way. The sidecut of the ski, and inconsistency in the sidewall worry me about keeping the intersect in the center. You are using a very accurate method based off the sidewall, which has curves, bumps, and errors. I prefer to measure straight across (eyeballing "straight across") with a ruler 5 times over the length of the template, then make a centerline from an average of those.
That's just my preference though. Both have proven themselves to work fine. We're just talking about mounting skis here. Its not nanoscience.