This is a very simple HDA. Please don't expect it to work for complexed structures.
The spark came from this thread, ie. there's wall and window frame, you can hole out the frame since it's a real object but how do you hole out the 'hole' of the frame as it's non-existent:
Note: it works with a 'solid' objects (watertight/thickness) not a paper thin object.
(updated to check centre of mass, you may need to redownload, sorry about that)
vu_neg_space.hdanc