This scenario has been tested the 21/12/2012 for a special science café at the Observatory of Florence
http://www.caffescienza.it/programma-2012-2013/la-notte-della-non-fine-del-mondo
Due to the large number of attendees, the meeting was split into three rooms, and we used a Google hangout to connect them. In the first room there were experts and the main projector. The pc for projecting slides served also for initiating the Google hangout. In each of the other two rooms, there was a pc, attached to the audio system, and a projector. The projector showed the same slides (screen sharing) as the main one, or the image of experts after the initial presentation. The camera of the pc was pointed on the public, so that people in the two auxiliary rooms could pose questions standing in front of the camera, and the experts (and the rest of the public) could see the questioner switching the view of the hangout. In each of the auxiliary rooms, a facilitator was present. This modality can be used for shared distant participation, where part of the public (or experts) stay in a different city.