OpenBridge Deck Slab - Keeping Soffit of Deck Slab horizontal (not following vertical curvature of the alignment)

Is there any way to allow the Top face of the slab to follow the curvature of the alignment (horizontal and vertical), but for the Soffit of the slab to remain level (horizontal, but vertical is fixed). Or for the slab to be placed to follow the horizontal geometry of the alignment only?