I don't known that having some fish, who busts in the first or second level, relog, rebuy and add to the prizepool is necessarily a bad thing. Just don't make the late reg retarded long.
like pokerstars in majors with 180-min latereg

I think ~15 minutes would be optimal (and I think micon had similar intentions because this allows the people who turn on their computer a few minutes
too late for a tourney still to enter).
And the percentage of people who bust in the first blind level (or maybe the second) should be really negliglibe.