Particle Smoke, Self-shadowing & light shafts?

In the Content Demo ‘Effects’ example I have been experimenting with cloud self-shadowing. I have been trying to produce this effect (light shafts in smoke):

https://dl.dropboxusercontent.com/u/15053325/SmokeyLightShafts.wmv

However, I am no sure whether it needs esoteric settings or is simply not possible.

I have already read these posts but no solution was forthcoming:

(1)

(2)

(3)

Let me know if you have any ideas.

Alternatively,

If particle smoke could produce light shafts from a DirectionalLight (in the same way that solid objects do)
then that solution would also be acceptable.