Hi,
Unfortunately, the RailClone plug-in cannot "unevenly scale" the used segment. However, you can use shorter segments and apply, for example, the Vertex Weld modifier to join them. Another possibility would be to directly adjust the base spline to achieve the desired shape (for example, with the help of the Wave modifier) and use that one for the other part with the RailClone plug-in and the inner part with the usual spline modeling techniques. Please find attached both approaches applied to your provided scene. I hope that helps.
Best regards,