  $V_{ub}$ is the smallest and least known of all CKM matrix elements; the
community currently determines its magnitude primarily through the exclusive
process $B\to\pi\ell\bar{\nu}$. Here we present our progress toward a lattice
QCD determination of the $V_{ub}$ matrix element from a novel transition --
$B\to\pi\pi\ell\bar{\nu}$ process, where the $\pi\pi$ system is in a $P$ wave
and scattering features the $\rho(770)$ resonance as an enhancement. We perform
our calculation on $N_f=2+1$ isotropic clover fermions on a lattice of
$L\approx 3.6$ fm and a pion mass of $\approx 320$ MeV; for the $b$-quark we
use the anisotropic clover action. After a brief overview of the theoretical
framework, we will discuss some preliminary results.
