  Polarized Compton scattering off the proton is studied within the framework
of subtracted dispersion relations for photon energies up to 300 MeV. As a
guideline for forthcoming experiments, we focus the attention on the role of
the proton's spin polarizabilities and investigate the most favorable
conditions to extract them with a minimum of model dependence. We conclude that
a complete separation of the four spin polarizabilities is possible, at photon
energies between threshold and the $\Delta(1232)$ region, provided one can
achieve polarization measurements with an accuracy of a few percent.
