3D depth map in front extruded from a flat back

Hello,  I am trying to create a 3d object that can be used to cut a foam shape from it.  I want to have a 3d depth map on one side and from the lowest point then be able to create a further depth of a set amount and then have a flat back.  When I create the depth map and you rotate it, you can see that the depth goes to the very back.  I have been unable to find a way to create a uniform depth from the base of the depth map and then have a flat back.  I want to know if this is even possible in photoshop. If anyone knows if there is a tutorial avaialble, if that is something possible.  First is the front second is the back.  Just wondering if I can extrude the front and make the sides have a set depth for printing purposes.