An auxiliary injection unit is disclosed that has an extruder barrel and extruder screw integrated within an injection molding system. The extruder barrel and extruder screw are contained within a mold plate of the injection molding system with a drive mechanism of the auxiliary injection unit being external thereof. A melt stream emanating from the extruder barrel of the auxiliary injection unit is in selective fluid communication with either a melt channel of a manifold providing melt thereto during an injection cycle or with a discharge channel of a melt discharge tube for purging melt. A melt diverter component receives the melt stream from the extruder barrel and includes a shuttle valve slidably positioned therein that is operated to selectively divert the melt stream produced by the auxiliary injection unit to either the melt channel of the manifold or the discharge channel of the discharge tube.