An interesting possibility to ease the tension between various determinations of $|V_{ub}|$ is to allow a small right-handed contribution to the standard model weak current. The present bounds on such a contribution are fairly weak. We propose new ways to search for such a beyond standard model contribution in semileptonic $B\to\rho \ell \bar\nu$ decay. Generalized asymmetries in one, two, or three angular variables are introduced as discriminators, which do not require an unbinned analysis of the fully differential distribution, and a detailed study of the corresponding theoretical uncertainties is performed. A discussion on how binned measurements can access all the angular information follows, which may be useful in both $B\to \rho \ell \bar\nu$ and $B\to K^* \ell^+\ell^-$, and possibly essential in the former decay due to backgrounds. The achievable sensitivity from the available \babar and Belle data sets is explored, as well as from the anticipated $50\,{\rm ab}^{-1}$ Belle~II data.