OneNote file migration to Sharepoint: How to convert multiple One Note 'folders' to 'files'

Description of what I mean by 'folder' and 'files' here: http://itgroove.net/oh365eh/2014/05/13/onenote-notebook-files-folders-work/

'Folder' is how you see a OneNote notebook in file explorer on a PC.
'File' is how Sharepoint converts those folders when you upload a OneNote notebook.

I am trying to migrate thousands of Notebooks to Sharepoint with the end-goal being these Notebooks should be accessible in the smartphone OneNote apps.
Only the OneNote 'files' can be opened on the app. The 'folder' files will instead prompt the OneNote app to create a copy.

The problem is that if I try to upload the notebooks within the web browser, it uploads them in the 'folder' format.

On an individual basis, it is very easy to move a single file to Sharepoint within One Note so it creates the 'file' format.
But when dealing with thousands of files, this would be too time consuming.

Is there any third party tool I can use which would exist in converting these Notebooks to the 'file' format either before or after they are on Sharepoint?
I have already tried contacting Microsoft support and a few other vendors but have come up short.