Transit Compartment Model for PK with Multiple Doses

All, Has anyone ever used a transit compartment model in NONMEM for PK with multiple doses. We are looking to use ~25 transit compartments (and thus ~25 DiffEqs in the $DES block). This seems easier for multiple doses, compared to the mathematical solution detailed in Rada Savic's 2004 PAGE presentation. We are also trying to implement the gamma scaling factor in the transit compartment equations (Sun YN, Jusko WJ. J Pharm Sci. 1998 Jun;87(6):732-7), but it seems to be fairly unstable in NONMEM. Can anyone comment/help? Thanks in advance, Matt