Create Camera Frustrum planes for specific layer

I'm using the Wiki's http://wiki.unity3d.com/index.php/IsVisibleFrom[link text][1] method to determine whether a renderer is seen by a specific camera. However, it doesn't account for the situation where the farClipPlane is layer specific, aka Camera.layerCullDistances. How should it be modified to use the layer-specific farClipPlane rather than the default farClipPlane?