Hi @nuklearwanze, thanks for dropping by.
Although we can't offer much input for third party apps, I wanted to mention that you can still use the desktop app to upload these files.
Instead of uploading them in one go though, you can do it in smaller batches and, once they sync, use Smart Sync and selective sync to save computer storage.
I hope this helps to some extent, but let me know if you have any other questions. Cheers!