We have a Document Library in SharePoint 2013 where we have set up some custom fields, such as Project Number, to help in organizing the documents. When we open up the library using Explorer View we'd like to be able to add some of these fields to the standard list of file fields (name, program, date, etc). I found a blog post on how to do this in SP 2008, but I haven't seen anything for how to do it in a later version.
Short answer is you can't.
Long winded answer is you would need to set up your document library to use folders under the hood (with or without setting up column default values). In the SharePoint view, you would configure it to show items without folders, but in the Explorer view, it would revert to the folder structur you would navigate through.