Hello there. This is currently driving me nuts! I've check a zillion different guides / docs and tutorials but cannot find an answer...if anyone could help me out here I'd be very grateful.

I need to render reflections from some objects that appear on a floor plane. I can set the reflection pass up / use a background layer in order to achieve this but I always get the outline of the plane appearing in the alpha channel. What I need is JUST the reflection colour and for the floor plane to be totally hidden ( just catch the reflections )

Probably best described with an image - see attached
I can composite over other layers no problem with blend modes, but I need this as a transparent PNG so I need to kill the background at render.