Всё оказалось проще. Результат такой, какой нужен. Запустил выложенный образец.
you need to unwrap your mesh but also manually split edges (V key) to match uv islands
then duplicate your object -because it will be overwritten- and in object mode run the snippet from a text editor
a quick example: https://db.tt/kWAzckzW
a proper script would need to be smarter, would take care of splitting edges, scaling result and adding it as a shape key