I don't have a Windows box handy to test with, but I'm fairly certain this won't work. When Windows/IE sees that it's got a generic octet stream to work with (and sometimes even when it doesn't), it will use the filename extensions to determine the document type.

For this to work, then, you would have to also change the filename to something other than .doc, package it into a ZIP file and have the user unzip it, or convince your users to use a browser other than Internet Explorer.