Wave,

  Never tried this configuration before, but SpectreRF
periodic stability analysis should be able to calculate
the stability characteristics of the circuit. To use,
1) Calculate the periodic operating point, that is, run
   autonomous PSS
2) Run Periodic stability analysis, pstab

In the past, I have used this analysis to calculate the
gain and phase margin of dynamic circuits, for example,
DC-to-DC Converters and VCOs. You just need to make
that you correctly define the loop.

                                              Best Regards,

                                                 Sheldon