  We study direct CP violation in $B^\pm \to \rho^\pm\rho^0(\omega) \to
\rho^\pm\pi^+\pi^-$ and focus specifically on the rate asymmetry in the
$\rho^0$-$\omega$ interference region. Here the strong phase is dominated by
isospin violation, so that it can be essentially determined by $e^+e^- \to
\rho^0 (\omega) \to \pi^+\pi^-$ data. We find the CP-violating asymmetry to be
of the order of 20% at the $\omega$ invariant mass. Moreover, it is robust with
respect to the estimable strong-phase uncertainties, permitting the extraction
of $\sin\alpha$ from this channel.
