Position Spline

[tyFlow]

Splines input into Position Object operators are converted into meshes, with each (interpolated) knot becoming a vertex (you can adjust the interpolation settings in the spline base-object itself). There are no extra interpolation options. The whole point of using Birth Splines is because it offers spline-centric functionality that other operators cannot

Maybe you can elaborate why that's not an option in your specific scenario...