PostgreSQL replication for archiving
Bucardo is log/trigger based as I understand it.  This means it doesn't require that other tables are not accessed.

The simple solution seems to me to create a trigger which inserts rows in these tables to rows in archive tables when they are inserted or, in the alternative, deleted.  This way everything works properly on Bucardo's side but you retain a copy of the full data elsewhere.

Actually a better option might be to move to an unreplicated partition on delete.  That way you still get a consistent view of the data as if the delete never took place.

Additionally if you have trouble making Bucardo work, Slony would be an option.