cnc scaning?

[EddyCurrent]

Take a side view photo then a plan photo of the board. e.g. http://www.mycncuk.com/threads/7823-...0995#post60995
Import into CAD and trace the outlines or use Inkscape (free) to trace them. Orient the traced outlines on the X and Z azes then do a '2 rail sweep' to obtain a solid 3d model, Rhino3D does this great.
Use the control points on the curves to fine tune your shape. There are videos showing this.

This one uses the similar 'surface from curve network' ;http://www.youtube.com/watch?v=BRRIBptfFxg

I'm thinking you could make accurate cross section drawings at various points along the surfboard and the CAD software would draw the in between parts to create the solid model.