There have been one or two users during the past 2-3 months who have posted questions that indicate they are doing what you're interested in doing. Hopefully one of them will chime in sooner or later with direct answers to your questions. I use Origin as a DDE "graphics server", but probably not the way you want to do it. I have an acquisition system based on a LabView VI that saves the data to file. When I want to send data to Origin for analysis the VI saves the data in a temporary file and sends a DDE command to Origin telling it to import the file. Not fancy, but I've found this method to be quite efficient. I'll give you details if you're interested.
Perhaps you read this already, but here is a link to the description of how our Graphics Export Server works: http://www.originlab.com/www/downloads/demo/graphexp.asp It's an Origin Pro version - usually the latest beta - plus two addon modules.