Hmmm. Still, the the same idea MAY apply.

The 'bright' area is from the baked light-map right? It looks like it...
See how the bright area is roughly rectangle-shaped.
So the 'width' is the door is the narrow dimension of that area.

What we need is a shadow-sprite to cover the light area.
Now when the door is shut, the shadow needs to cover the whole bright-zone.
But as the door opens, we need to shrink the scale of the shadow in the
narrow dimension of the shadow, so the bright-area gets slowly exposed.
You will also need to shift the shadow sideways toward the hinges-side of the door,
so that the bright area only only gets exposed on the non-hinge side of the door.

Unfortunately I cant do pictures at the moment, otherwise I would do a diagram...

I hope this explains my idea...