ADT7470: disable pulse stretching in LF-PWM mode


I'm using the ADT7470 for auto-controling a simple 2-wire fan without tach.
In the recommended low frequency PWM mode the ADT7470 adds some pulse stretching that is audible when the fan is running :-(
I don't need pulse stretching since I'm not using any Tach signal.
Is it possible to disable pulse stretching in low frequency mode or is there any workaround?