Around hereabouts (Boston), dancers have been observed lining up duple improper. I'd say that is a good bet upwards of 98% of the time. Usually the cross-over makes it halfway down before some cajoling from the downstream dancers gets the cross-over the remaining way. If you train the dancers to take hands four in improper circle as they join the set, then the sets will be comfortably spaced out, as well. Worth trying, I think.
As a dancer or floor manager, I sometimes have done what the Scottish Country Dancers do: An individual from the top couple walks down the set and counts people off. Instead of "1, 2, 3, 4: end of set; 1, 2, 3, 4: end of set; ..." it would simply be 1, 2, 1, 2...
