[hex4def6]

This seems like a job for a truecrypt style system. Either you do it at a file-level, or you have it split into (say) 10MB file chunks, and if you want to access a certain file you have an encrypted local db that acts as a magic decoder ring ("file test.csv is spread across CLOUD1.DB CLOUD3443.DB CLOUD132.DB").

Combine that with steganography (Enter real_password, and test.csv is a list of bank accounts, enter fake_password, and test.csv is a list of apple store locations, enter random_password, and it decodes junk). Maybe combine that with multiple layers of passwords (one ring to rule them all, except certain files).

Obviously, you'd want to steganographize the decoder ring as well.