If you are lucky enough to own one of these beauties you may be interested in
making one of these, I have the parts arriving today complete with Cokin ND4 filter.
The down side is that the darkest Cokin do in the X-Pro series is ND4, but you can double them up to get even slower speeds.
All parts including ND4 filter £152. The Lee SW150 costs £300 so quite a saving for very little effort.
Bob
PS thanks to Reed Ingram for the Excelent idea and parts list
PPS there is complete coverage at all 14-24mm so the entire zoom range is covered by the filter on my D3s (FX)