Hi,
what kind of discrete components would you like to include in your 3D calculation.
If you are only interested in passive devices (R,L, C and maybe diodes) CST Microwave Studio could handle this directly.
For active components, you would have to split the simulation in two parts. One for the 3D simulation in which you replace the active elements by ports. You could then use the generated results (S-Parameter) in a circuit simulator.
Hope this helps,
Frank