Does anyone know if it is possible to make our own floor in SolidWorks (with a displacement map, for example) and have it render without that floor emitting alpha?

Specifics: I'm trying to render a boat (with some glass) in the water, and insert it into an environment image with Gimp or Photoshop. I can see how to use the Floor Shadow and Floor Reflections options in the PV 360 Scene area, then save out the Alpha channel for a layer mask, but I can't seem to find a way to have that floor have displacement that would create rough shadows/wavy reflections. The problem I'm running into is that when I make a floor out of a solid part, that "floor" part radiates Alpha, making it difficult to crop out the important part of the image. While I can make a material render nearly black by turning down all emissions, it still comes out white-hot in Alpha.

Thanks for any help!