A combined venture would be an interesting experience, which needs however a lot of extra organisational effort. Just to do it for those few who have registred but didn't make would not be efficient. If we want to do it then it should be an event (or series of events) in its own right.
If any one is interested in first hand account of doing a virtual event coupled w/ F2F event, I was part of a team (out of http://www.bigmindmedia.com) who did this recently for the International Appreciative Inquiry Conference. We learned a *lot* of lessons. There is definitely possibility in this practice to link up those who would not otherwise be able to come F2F (cost, visas, etc.) The biggest questions I came out of it were: * We can design a pretty damn good experience capturing the F2F for the distributed participatns. Do we want to and if so how do we do the reverse for the F2F? (Goes to fraccination of the audience?) * What did we learn from both elements that would inform design of group events in general (online and offline) - in other words, what past assumptions can we see in a new light? (LOTS here) * What does it really cost (we are working on that number now.) If you want to know more, feel free to contact me offllist.