  We present designs for the augmentation 'mirror' pulses of
large-momentum-transfer atom interferometers that maintain their fidelity as
the wavepacket momentum difference is increased. These bi-selective pulses,
tailored using optimal control methods to the evolving bi-modal momentum
distribution, should allow greater interferometer areas and hence increased
inertial measurement sensitivity, without requiring elevated Rabi frequencies
or extended frequency chirps. Using an experimentally validated model, we have
simulated the application of our pulse designs to large-momentum-transfer atom
interferometry using stimulated Raman transitions in a laser-cooled atomic
sample of $^{85}$Rb at 1 $\mu$K. After the wavepackets have separated by 42
photon recoil momenta, our pulses maintain a fringe contrast of 90% whereas,
for adiabatic rapid passage and conventional $\pi$ pulses, the contrast is less
than 10%. Furthermore, we show how these pulses may be adapted to suppress the
detrimental off-resonant excitation that limits other broadband pulse schemes.
