Is there a way to include the Evernote Web Clipper as a plugin into K-Meleon?

The only way is the bookmarklet. Copy the code below, create new bookmark in Personal Toolbar Folder using Bookmarks manager and paste the code as the URL.

javascriptfunction(){EN_CLIP_HOST='http://www.evernote.com';try{var%20x=document.createElement('SCRIPT');x.type='text/javascript';x.src=EN_CLIP_HOST+'/public/bookmarkClipper.js?'+(new%20Date().getTime()/100000);document.getElementsByTagName('head')[0].appendChild(x);}catch(e){location.href=EN_CLIP_HOST+'/clip.action?url='+encodeURIComponent(location.href)+'&title='+encodeURIComponent(document.title);}})();

Then just press the created bookmark on toolbar and you'll get the WebClipper.
(you may probably need to add cookie allow exception for evernote.com - if 3rd parties are disabled in your KM)

working webclippers (bookmarklet-based) for

Evernote

Pocket

OneNote