Waveform controller aleternative

I there.
I am trying to mimic breathing animation. so i made a morph target for breathe in position and gave it a waveform controller. The problem is that, I want to alter waveform_float controller's period (or wave frequency) during animation.I made a control object, and tried to wire position of the control object to waveform_float controller's period parameter. But I can't do it because it is not revealed in wire parameters dialog. Is there a workaround for this via scripted controllers.
Thank you.
Edit: I have made it with a simlple expression controller
abs (sin (F*pos)*100)
where F = frame pos= y position of the controller object(scalar value) and abs is absolute value funciton