  The early inspiral of massive stellar-mass black-hole binaries merging in
LIGO's sensitivity band will be detectable at low frequencies by the upcoming
space mission LISA. LISA will predict, with years of forewarning, the time and
frequency with which binaries will be observed by LIGO. We will, therefore,
find ourselves in the position of knowing that a binary is about to merge, with
the unprecedented opportunity to optimize ground-based operations to increase
their scientific payoff. We apply this idea to detections of multiple ringdown
modes, or black-hole spectroscopy. Narrowband tunings can boost the detectors'
sensitivity at frequencies corresponding to the first subdominant ringdown mode
and largely improve our prospects to experimentally test the Kerr nature of
astrophysical black holes. We define a new consistency parameter between the
different modes, called $\delta {\rm GR}$, and show that, in terms of this
measure, optimized configurations have the potential to double the
effectiveness of black-hole spectroscopy when compared to standard broadband
setups.
