Fading shadows in / out along with material.

I have the following setup:

• A cube with standard shader.

• A plane, below the cube, also with standard shader.

• A single directional light, rotated in such way that the cube casts a shadow on the plane below it.

I'm trying to do the 2 following things:

1. Fade in / out the cube material, in such way that the shadow cast by the cube also fades in / out with the cube.

2. Fade in / out the plane, in such way that the shadow cast on the plane by the cube also fades in / out with the plane.

So far I've tried both the Fade and Transparency modes and neither seems to accomplish this. That is:

1. If I do Fade / Transparency mode on the object casting the shadow (the cube), the shadow stays at full opacity regardless of what I do with the material's alpha.

2. If I do Fade / Transparency mode on the object receiving shadows (the plane), shadows go away completely on the object; it no longer receives shadows.

I'm just wandering if there is a way to accomplish what I want.