How to simulate pnoise of fractional (non-integer) frequency divider

Hi there, I tried to simulate pnoise of the frequency divider with a divider ratio of 4.5 (non integer value). however, I have a hard time in setting the beat frequency to be Freq_in/4.5 with relative harmonic = 1, as it complaints about the fundamental tone (=Freq_in) must be integer multiple of beat frequency. The cadence version that I use is ICADV12.3 and MMSIM version is 16.1.0.479.isr9. Thank you in advance for all your replies. Yin