I have updated the Silverlight "Surface" demonstration with video support [1], too. The only thing I had to do is to replace the Silverlight.js JavaScript file and change the boolean properties in the createObjectEx to their string representations (true becomes "true").
Inside the .NET source I had to remove the third parameter for the Open method of the downloader object. With the new bits all requests are done asynchronous, so there is no real need of this parameter (see the same change in the JavaScript part of the plugin at Joe Stegman's post [2]). I run my build.bat and everything is working.