Thickness of curves in rendered image

Dear all,
using the settings, the thickness of the surfaceisocurves in the rendered view in Rhino can be set and it is displayed accordingly. However, when the image is actually being rendered, no lines are visible. If in the effect panel “curves” are activated, the lines appear but with a thickness of always 1, no matter what was set in the settings.
For my purpose it is important to keep the curves visible and I hope you can help me to find the setting to set the curve-thickness in the final rendered image.