I don't know why you wouldn't also filter the Top N providers, since
most of the huge problems have resulted in poor filtering between
large providers. A small provider can't really have much of an impact
on the net unless their bogus announcements are propagated. Its the
propagation of bad information which turns it into a worldwide problem.
As to your question. Try searching for discussion about "access-list 112"
It will be a bit heated, but you'll find a few usefull tidbits in there.