My initial idea was to include the towns of San Francisco, Davis, Placerville, Chico and Sacramento. These are the cities nearest to Sacramento with groups, that I found. If you know of others in a reasonable distance, please let me know.
Then 4 of the cities could invade the 5th. At this point, I suggest that we NOT invade SF. They are invaded daily, and finding the needed number of couches would be nightmarish, although I have no doubt my 2 city ambassadors and my friendly country ambassadors, all living in Sac, could help us out. But why not invade Davis, Placerville, Sacramento or Chico? Then, we could invade the next city... and the next... like every 3 months or so. :)