I'm working with a local highschool on building skateboards. The students will be designing the entire board up in solidworks and then pressing the boards, creating a CNC toolpath and then cutting them out. I have used the tutorial from http://www.cudacountry.net/html/sw_skateboard.html and have had no problem creating the model. My problem is creating the male/female molds to be used in their hydraulic press. I get to a point where I loft the entire surface of the deck but it is only as wide as the board (9"x33"), but I need to somehow extend the surface to be about an inch or two longer in every direction to accomodate the pieces of wood that will go into the press (12"x36") which will be trimmed down to size on the CNC.

Is there any way to create say a 12"x36"x5" rectangle and then cut my surface into it, but have the concave and shape extend out?