extrude curves on polysurface

Hi all,

As the title says, I'm basically trying to extrude many curves OUT from a curved polysurface, using the direction of the face (normal direction?) as the direction of extrusion.

Here is exactly what I want to do, but with many curves and a polysurface, it is the 'Fin' command in Rhino. Scroll down to Fin:

http://www.rhino3d.com/4/help/commands/extrudecurve.htm

I think this is a simple one, but I'm just starting with grasshopper. Any help would be much appreciated!

thanks