We propose a new method for analysis of nonmonotonic forced Rayleigh scattering (FRS) decay profiles. It is shown that the curvature near the local maximum of a decay-grow-decay profile or a grow-decay profile can be used to determine directly the geometric mean of the unperturbed and photoproduct diffusion coefficients, which will in many cases mitigate the need to apply multiparameter nonlinear fitting routines. FRS tracer-diffusion measurements of methyl red in poly(vinyl acetate)/toluene solutions at two different probe wavelengths, analyzed using the new method, are in good agreement with results of previous studies. Simulations are used to estimate the systematic error due to the approximation employed, and it is concluded that accuracies of a few percent or better should be routinely achievable in most cases. We have, in addition, investigated the probe-wavelength dependence of the profile shape for this system.