There was no way to add this that would be efficient with the current implementation method.
The Expander device remains a target for future work. In particular, it has two real jobs:
- Grow/Shrink/Simplify the spatial extents of masks
- Alter the shape of a terrain
The same algorithm is used to do both right now, but seperating their function into two different devices would allow for a much more efficient implementation for #1, and more options for #2, including this suggestion. This remains as something I’d like to do.