Connect in series 2 DC sources:
One of them has Vdc=Vgate Vac=0
Another Vdc=0 Vac=1m
Use AC analysis and change Vg as sweeping parameter.
Then plot C= Ig/(2*Pi*Freq*Vgs) vs. Vgate. You will get CV curve.
I did that several times in Cadence. It works fine.
There is another method using transient with fixed frequency.