This is the very basic setup for a winding track, for any one who hasn't found it yet. Just make your own track mask (greyscale tiff, Photoshop) and call it in the image map shader. Make sure the values in the image map shader correspond with the size rate of the tiff. You can extend this principle with more tracks blended together and different warp shaders to get them crossing each other, and so forth.
Thank you Ulco, This is something I will try.
Dune i didn't quite understand what this was at first.
I just tried your file.
Thanks a lot :)