if you have a curve you need to make a parallel to, like for making a two part form for bent lamination, a common trick is to use a washer. you run the washer along the reference curve and your pencil in the hole in the washer. this gives you the parallel curve offset by the width of the solid part of the washer.
This sounds even better. I was imagining a similar idea where for every point in the Bezier you have a normal that can extend both directions by a specified amount. The smoothness still requires some interpolation which shouldn’t be too further from normal Bezier interpolation.
