I just updated GhGL to support preview sort order so you can do this.
Here is a sample definition to start with
sorted_curves.gh (29.0 KB)
If you right click on the “GL Shader” components, the context menu will give you access to “Preview Sort Order” and “glLineWidth”. Use the “Preview Sort Order” to define which curves will be drawn before other curves. This is necessary to get things like alpha blending to properly work. Use the “glLineWidth” to adjust the width of each curve.