  We use self-consistent field theory to determine structural and energetic
properties of intermediates and transition states involved in bilayer membrane
fusion. In particular, we extend our original calculations from those of the
standard hemifusion mechanism, which was studied in detail in the first paper
of this series, to consider a possible alternative to it. This mechanism
involves non-axial stalk expansion, in contrast to the axially symmetric
evolution postulated in the classical mechanism. Elongation of the initial
stalk facilitates the nucleation of holes and leads to destabilization of the
fusing membranes via the formation of a stalk-hole complex. We study properties
of this complex in detail, and show how transient leakage during fusion,
previously predicted and recently observed in experiment, should vary with
system architecture and tension. We also show that the barrier to fusion in the
alternative mechanism is lower than that of the standard mechanism by a few
$k_BT$ over most of the relevant region of system parameters, so that this
alternative mechanism is a viable alternative to the standard pathway.
