Wow it seems like they already removed JSON export. I just downloaded the app to see. I just went through the migration with my coworker last week so I'm surprised it's gone so fast. I'm not sure if you can get a hold of a slightly older version that allows the JSON export.
If you export all notes to HTML, I might be able to help. I would need to rewrite my script a little bit. Just lame since the JSON was way easier. Maybe their product management people saw this thread and disabled the JSON export to get one over on people jumping the Nimbus ship...lol...