From what I understand ipfs add does cryptographical magic, and chucks the original file into the IPFS_PATH. I wonder, was it ever considered not to physically chunk the file, but rather describe the meta data to chunk the original file on the local file system preventing the duplication on the first node.
I believe what you’re describing is FileStore, where the data isn’t duplicated. Once enabled you can utilise it with:
ipfs add --nocopy <filepath>
Hope that helps!