Holding it somewhere near one of the Bay Area, Switzerland, Minnesota, or some exotic place Alexandre wants to travel to will increase the likelihood that he will be there.
If it'd be in August then I'd vote for Switzerland. It's pretty close to France/Germany, not too far away from England, it's "neutral" in that I think everybody would have to do at least some travelling to get there, and more to the point I have been intending to travel throughout August/September and was going to pass through Switzerland at some point.
So, I think that'd be a good place to hold it :) Still, Switzerland is quite an expensive country, that may make it too dear for many :(