Get Filename from Upload Popup

I am testing the monitoredExtensions.  I added extensions like exe, pif, bat, cmd, etc and when I upload a file with an exe extension I get a response that the file is not allowed-illegal extension--works great!!  However I find that the file must be uploaded first for the check to happen, which can take a minute or two (or longer depending on file size).  What I want to do is take the filename directly from the Upload popup dialog and check it BEFORE the upload.  How can I get the filename from the popup??

Thanks, Mike…