Saving and pasting a region with a complex shape (non-cuboid)

Plugins Plugin Development
1

So, I want to save region of blocks manually, block by block, because of it’s complex shape (and then saving it to HDD/pasting it with one command). But I have trouble doing that, because ArchetypeVolume can only be created by copying cuboid from Extent, and can’t be modified, or copied with a mask, or something.
Block by block creation works for MutableBlockVolume, but I can’t paste it in the world with one command, nor can I create ArchetypeVolume/Schematic from it, so I can’t save it.

Are there any existing solutions for that? I suppose I can paste manually, but I still have problem with saving to disk.

Edit: It seems like my issue was solved in a new SpongeAPI. I’ll test it tomorrow.

Sponge Build: n/a (cloned, SF 5.0.0-SNAPSHOT, commit 1492705)
Forge Build, Java Version, Forge Logs, Minecraft Logs: n/a (not a bug)

Plugin Source:

Vector3i maxSize = new Vector3i(10,10,10);
MutableBlockVolume blockVolume = game.getRegistry().getExtentBufferFactory().createBlockBuffer(maxSize.mul(2).sub(1,1,1));
// ...
blockVolume.setBlock(regBlockPos, fillbs, Cause.source(myPlugin).build());
// ...