  We present a continuous-time Monte Carlo impurity solver for multiorbital
impurity models which combines a strong-coupling hybridization expansion and a
weak-coupling expansion in the Hund's coupling parameter J. This
double-expansion approach allows to treat the dominant density-density
interactions U within the efficient segment representation. We test the
approach for a two-orbital model with static interactions, and then explain how
the double-expansion allows to simulate models with frequency dependent
U(\omega) and J(\omega). The method is used to investigate spin state
transitions in a toy model for fullerides, with repulsive bare J but attractive
screened J.
