Hmm! that's an unusual one
Making the assumption that you are still on 4.6 SS or below you could try to add them to database directly.
(Know doubt you could with 4.7 but I do not know that DB structure)
Get into db.view and examine the tables podcast_channel and podcast_episode.
From there you are on your own but I would imagine its the status columns (where it say's completed) is the one you are after.
