The instance I discribed above was practiced by Vladika Mitrophan in his parish church. I think he employed a sort of economia, because I hardly think it's fair to expect that a priest after a long vespers should actually stand there and confess 40-50, and sometimes more, people one at a time. That's not counting the 20 or so children. As it is it took forever to get thru just the absolution part. I remember still standing there at 11 one night and he still had a bunch to go. I remember another priest who did individual people on such a occassion, they were still there are 2 in the morning. Many ended up not going to communion or coming back in the morning for confession...which just held up the service. Even if he had started early(which he did), he could not have done it in a timely manner. That is why I believe Vladika required a previous full confession before coming to this "general" confession. I think that even Fr Seraphim would find nothing wrong in doing it this way.
And by the way those who tried to "sneak in" were always caught and had to do a longer confession anyway once they got up there. Rather embarassing as everyone knew your "offense" then.