  We show that the tunable hybridization between two lateral quantum dots
connected to non-magnetic current leads in a `hanging-dot' configuration that
can be used to implement a bipolar spin filter. The competition between Zeeman,
exchange interaction, and interdot tunneling (molecular hybridization) yields a
singlet-triplet transition of the double dot {\it ground state} that allows
spin filtering in Coulomb blockade experiments. Its generic nature should make
it broadly useful as a robust bidirectional spin polarizer.
