Hey, if you look at this post, you should be able to get started:
Volumetric Clouds page-11#post-7666078
Your LUT will need to contain every possible vertical slice of the “duck” you want to paint.
I can warn you that you might struggle to do this. The volumetric cloud system is really designed to produce stratus, cumulus and cirrus clouds (and any subtypes), it hasn’t been designed to produce complex arbitrary shapes.