Oh I see. I didn't actuall watch the video.
However, it's easy to mock. It's only occurring in direct lighting, and you can modulate that with colour. So you can literally use a 3D simple shape and put it up somewhere you'd want the effect, make it soft, and make a colour map, warp it by the clouds scalar as displacement (smoothed with smoothing function) to follow its structure, then smooth possibly, and you might have something.
Probably use final position for noise and modulation maps.
