We simulate the phase separation of binary mixtures under shear in the presence of solid, mobile particles. We combine cell dynamical equations for the binary mixture with Langevin dynamics for the particles and carry out the simulations in two dimensions. One of the components preferentially wets the surface of the particles. In the initial stages of the evolution of the microstructure, the morphology of the domains is isotropic. At later times, the domains grow faster in the shear direction than in the perpendicular direction. For sufficiently large particle densities, however, this anisotropic growth is destroyed by the randomly moving particles, and the domains are isotropic in shape even for large shear strains. Thus, solid additives can be used to tailor the morphology of the mixture and thereby control the mechanical integrity of the composite.