Ansoft designer - working with variables problem

Hi everybody! I have a little problem with a simulation of a system on Ansoft Designer v3. I'm trying to simulate a system that have a VCO, so I've used the VCO block avaiable on the software, but the gain of my VCO is not constant, it changes following the equation

where K is the gain of VCO
ko and kn are constants
Vin is the input voltage of my VCO

My question is: How can I put this expression in the k parameter of VCO? I couldn"t do because i don't know how to measure Vin(t) and use it to compute the gain.

Can someone help me?[/tex]

if k0 and kn is const, make kn=0, so K will depend only from k0.