We analyse the non-universal conductance fluctuations for a dirty quantum wire in a transport regime where both mesoscopic and ballistic transport characteristics play a role. This `mixed' transport regime is reached when impurities are distributed near the walls of a quantum wire, leaving the centre region ballistic. Using a diagrammatic technique, we find that the existence of a ballistic region destroys the conventional universal conductance fluctuations. The crossover behaviour of the fluctuation amplitude from the usual quasi-1D situation to that of the mixed regime is clearly revealed, and the role of various length scales identified. Our analytical predictions are confirmed by a direct numerical evaluation of the Landauer-Büttiker formula.