Solved! Go to Solution.
I made a solution that measures your original spline poles from the Y constant plane and creates contruction curves from the sketch points down along Y at the measured values. Then make a new spline through the end points of the construction curves.
Probably more complicated than you hoped for and I'm sure your real model is more complicated. This can be easilty automated with some code to make it super effecient.
you can create construction lines through the sketch points and normal to the sketch plane. Then you can use the end points of the lines to create a associative spline.
Production: NX10.0.3, TC 10.1.4