These two papers published in 2010 contain additional material on the relativistic dynamics and on the computation of the observables for a very high accuracy orbit determination experiment:
Milani, A., Tommei, G., Vokrouhlický, D., Latorre, E., Cicalò, S.: Relativistic models for the BepiColombo radioscience experiment. In: Klioner, S., Seidelmann, P.K., Soffel, M. (eds.) Relativity in Fundamental Astronomy: Dynamics, Reference Frames, and Data Analysis, IAU Symposium, 261, 356-365 (2010)
Tommei, G., Milani, A. , and Vokrouhlický, D. : Light-time computation for the BepiColombo Radio Science Experiment, CMDA, in press.