This request is in regards to surfaces set to none or invisible blocks. I mentioned sprites because I don't know if the shadow would appear on top of the sprite and blend with it or if the sprite would cover up the shadow since it's in front of the hidden geometry the shadow is supposed to appear on.

These sprites would only appear in places where the player could walk behind them. The stove in the image above is a good example. As pictured above you can only walk in front of it, but if it were placed in such a way that the player could walk behind it, I'd place a sprite in front of the hidden geometry representing the stove.