I haven't seen their code, but I'm not sure why you'd need server side DOM manipulation for this. I'd implement all of that in the browser, and just let the server handle passing events back and forth.
Since they're proxying the page, they replace all <a>s with proxy <a>s, as well as adding a <script> and a <div> with some content to the bottom. Try viewing source on http://starcraft2destroyedmymarrage.no.de:3000/app/4