This is a major kludge, but will do the trick. First install the bookmarklet from this answer.
javascript:window.location="https://gmail.com/#search/rfc822msgid:"+encodeURIComponent(window.document.body.innerHTML.match(/Message-ID: <(.*)>/)[1])+"/"+encodeURIComponent(window.location.search.toString().slice(1).split('&').filter(function(x){return x.slice(0,3) == "th="})[0].slice(3));
Then follow these instructions.
- Click the menu button to the right of the message's "reply-to" button and select Show original.
- After the message's raw source is shown on a new tab (it will resemble the below screenshot), click the bookmarklet.
- A new tab will now open with the regualrly formatted message. You can now bookmark or copy the message's URL.
"shift-click"
the email in the Inbox list, it should open the message in a new window. You should be able to grab the URL of that window to get a direct link to that message.