We investigate the single-photon double ionization of molecular hydrogen theoretically over a wide range of photon energies. Our numerical approach is based on the half-collision picture of single-photon multiple ionization and employs a mixed quantum-classical method that splits the double ionization process into a shake-off and a knockout part. We demonstrate that this approach, which has been applied to the double photoionization of helium before, can be successfully extended to the case of molecular target systems with two separate nuclei. The treatment given here allows for both a computationally simple way of calculating molecular double photoionization in reasonable agreement with experiment and recent ab initio calculations, and a physical understanding of the results in terms of a simple quasiclassical picture.