[Koha] eBook marc records and subject headings

Greetings all, I have had a query from a school that receives brief marc records from their eBook vendor that do not contain subject headings but have an embedded url with online authorisation; they also have a subscription with a cataloguing company (SCIS in Australia) that can provide (some) full records with subject headings for eBooks. I am trying to determine the best workflow to add subject headings and would appreciate any advice or suggestions. At the moment I can only come up with adding the subject headings manually, one item at a time which is not ideal. Many thanks, Clint Deckard.