[Wild thought] Create a file with a list of H(chunk) forall chunk you own. You encrypt this file with a local password that the storage provider does NOT see and plainly store it.
I re-read the paper, and they seem to be doing what you describe. The list of H(chunk) is called "Chunk Map", and local password is called "dedicated map key"...
.. but after that they get into another round of encryption with the users public key - that's where I get lost.
[Wild thought] Create a file with a list of H(chunk) forall chunk you own. You encrypt this file with a local password that the storage provider does NOT see and plainly store it.