[Question] Going backwards (SplineController)

[Warow]

Hi, I would like to know if there's a way to make the SplineController follow the spline backwards dynamically.

I can see in the Move tab that there's a field named "Speed", but this is a absolute value, for example, if I set it to -1, it's considered 1 instead.
I want be able to change it's direction at runtime, doing so, I would like to tweak this values in a range like -100 and 100.

Thanks,
Luis