Import gizmo in Nuke with File ⇒ Insert Comp Node
This scripts works mainly with the Normal Pass using the IDistort nodes it allows to deform a shape, working with these informations you'll be able to add fake volume-deformations on simple shapes without any render;
To achieve that we need to work a little bit with Nuke's Expressions to use the potential of the R, G and B values of our Normal Pass, to make it easier the node have some Preview checkboxes so you can preview what you're writing, activating the High Quality Blur will be a bit more time consuming but result is way better.
Here we're working with ;
|Diffuse Map||Normal Map||Simple rotoPaint Mask|
Here is the result ;
If you have any questions... =)