In my relatively limited experience flying Continental I have already had a case where no upgrades cleared for platinums flying off-peak flights we took with non-elites (even though we separated the records before the upgrade window).

Are you saying that one needs to book each of the tickets separately by each passenger logging in separately? If a large # of passengers are involved, there's a real danger of the fare being increased if one attempts to book this way - these days the airline fare optimization software may very quickly reprice the itinerary before the last of the tickets is booked.