The phase separation dynamics of immiscible polymer blends is sensitive to applied fields (e.g. electric, gravitational, or flow) and surfaces which break the isotropic bulk symmetry. Here we consider the case, commonly encountered in applications, of filler particles added to a phase-separating polymer blend. The polymer-filler surface interactions preferentially attract one of the blend components, which leads to transient spherical composition waves about the filler particle. We predict the spatial and temporal extent of these patterns as a function of quench depth, molecular weight, and additive size. The presence of additives can significantly affect the phase separation morphology at intermediate times, especially for deep quenches, i.e., highly immiscible blends.