Nintex Forms - Document Library with multiple Content Types - Choosing a Content Type on Upload

Hi all, 

I have a SharePoint Online Document Library with multiple Content Types.
 

When I go to upload a document to the library, as expected, the document uploads as the default Content Type and I'm prompted to complete the metadata.
 

The issue I am having is that I cannot locate a change Content Type control in Nintex Forms (for 365). On the left in the image at the bottom is an Add a document dialog - Nintex Form version, on the right a SharePoint version. In the SharePoint version I can select the Content Type, in the Nintex version I can't choose a Content Type.
 

Unless I'm mistaken, it looks like there's no way for users to choose the Content Type when uploading a document to the Document Library if I've got multiple Content Types and a customised form for each Content Type. 

Does anyone know a workaround, or can let me know if there's something I'm missing here?

Thank you!