eli0s Your try is beautiful indeed.
This was the relevant part of the link I provided, a serie of demos with real-time volumetric lighting effects in AS3.
What I'm trying to achieve is similar to yours, I think. Please take a look at my example. It's an early test with some debug features, it lacks of a sun sprite and the sun that will be added is now represented by the position of the mouse. I'm trying to build a setup where shadows are not shown but only sunrays are, if they're not blocked by something (the clouds more importantly and the dragon maybe).
It looks like you put the collision mask in a strange way that it pleases me very much.
These are my collision masks, at the moment.