  Decay-time-dependent $CP$-violation effects in transitions of neutral $B$
mesons to $CP$-eigenstates can be visualised by oscillations in the asymmetry,
as a function of decay time, between decay yields from mesons tagged as
initially having $\overline{B}$ or $B$ flavour. Such images, for example for
$B^0 \to J/\psi K^0_{\rm S}$ decays where the magnitude of the oscillation is
proportional to $\sin(2\beta)$ with $\beta$ being an angle of the
Cabibbo--Kobayashi--Maskawa Unitarity Triangle, provide a straightforward
illustration of the underlying physics. Until now there has been no comparable
method to provide visualisation for the case of decays to multibody final
states that are not $CP$-eigenstates, where interference between $CP$-even and
-odd amplitudes provides additional physics sensitivity. A method is proposed
to weight the data so that the terms of interest can be projected out and used
to obtain asymmetries that visualise the relevant effects. Application of the
weighting to $B^0_s$ decays, where effects due to non-zero width difference are
not negligible, provides a novel method to observe $CP$ violation in
interference between mixing and decay without tagging the production flavour.
