Please take a look to https://archive.org/details/spinoza_etica_paravia_djvu
, this is precisely a djvu-only item that I uploaded some days ago. I asked for permission to create "djvu-only items" into IA forum and I got it; this is the fiirst item I created; as you see there's some "implicit convention" too (the name of item is the original one + a _djvu suffix: it has been derived from https://archive.org/details/spinoza_etica_paravia
) and metadata are the same, but a standard warning "Derived from files into L'Etica
" into the description field.
So far I did not do the last step, t.i. adding a "backlink" from original item to the derived one.
internetarchive.py allows to automatize the whole work (to download metadata of source item, to build the new item name and to add the warning do description field and to upload the new item).