Background passthrough per Alpha channel?

[MonroePoteet]

Is there a way to have LW move pixels from the background image into the final image based upon the value of the alpha channel? The issue occurs when a front-projection object is used with shadow density and the diffuse/luminosity values on the object cause its outline/surface to appear in the rendered image. I wrote an Image Filter plug-in to perform this functionality, which eliminates the final compositing pass, but I'm wondering if there's a native way to do this in LW?

Thanks,
mTp