soft shadows and accumulation buffer

I have created soft shadows by jittering lights…
I draw the entire scene and accumulate it then
I slightly move the light and I redraw the entire scene.
Finally I return the scene composed by the accumulated frames.
The problem is that I redraw the entire scene
even if only the shadow must to be redrawn.
Is possible to redraw only the shadow??
I want to draw the objects only once and then
I want to use the accumulation buffer for the lights.

Is possible to redraw only the shadow??
What do you mean? Can you post your code?

maybe you can use the stencil buffer to mask regions that don’t need to be drawn at all