  Within the widely used EvtGen framework, we have added a new event generator
model for $B\to K^* \ell^+ \ell^-$ with improved standard model (SM) decay
amplitudes and possible BSM physics contributions, which are implemented in the
operator product expansion in terms of Wilson coefficients. This event
generator can then be used to investigate the experimental sensitivity to the
most general BSM signal resulting from dimension-six operators. We describe the
advantages and potential of the newly developed `Sibidanov Physics Generator'
in improving experimental sensitivity of searches for lepton non-universal BSM
physics and clarifying signatures. The new generator can properly simulate BSM
scenarios, interference between SM and BSM amplitudes, and correlations between
different BSM observables as well as acceptance bias. We show that exploiting
such correlations substantially improves experimental sensitivity. As a
demonstration of the utility of the MC generator, we examine the prospects for
improved measurements of lepton non-universality in angular distributions for
$B \to K^* \ell \ell$ decays from the expected 50 ab$^{-1}$ data set of the
Belle II experiment, using a four-dimensional unbinned maximum likelihood fit.
We describe promising experimental signatures and correlations between
observables. The use of lepton-universality violating $\Delta$-observables
significantly reduce uncertainties in the SM expectations due to QCD and
resonance effects, are ideally suited for Belle II with the large data sets
expected in the next decade. Our simulation studies also show that Belle II
should have excellent sensitivity to BSM physics in the Wilson coefficients
$C_7$ and $C_7'$, which appears at low $q^2$ in the di-electron channel.
