You can do a path mate between a vertex and a spline. The spline can be in a sketch in the assembly or in a part.
Thank you for your help. I found a glitch in SW that wouldn't let me select the spline with the screen view split into 2 windows. If I rotated the one view 180 degrees, normal to the sketch, I could select the spline. When I went back to one view, I could select the spline from any angle.