text: Done in http://www.openstreetmap.org/changeset/37271826
  
  Maybe take a look and make sure I didn't miss any connections.
  
  There's no trick or good way to do it, I split the existing way where the divided road starts, moved the existing nodes to one of the sides and then added a new way for the other side and copied the tags. Then I moved along and checked/fixed the connections to the side road.