Vertical Navmesh?

I have a 2D game that looks like a top down, but actually is side on in the default 2D view. Behind the main graphics and components I have a plane, which is vertical, and cubes sticking out of it (that aren't visible) in an attempt to create a navmesh so that agents could walk around the area. Unfortunately, the navmeshes are created on top of the cubes, not on the vertical plane. Is there any way that I can make the navmesh generate on the vertical face of the plane? Thanks in advance