Animator speed problem

Are in different layers may be used at different speeds
I want use different speed between MainLayer and MaskLayer
I queryed API ,but not found

The speed of the animation can be set in the Animator Controller by selecting an animation node. In the inspector, you should see a setting for speed.

Thank you ,
I know this.
But I want to dymanic controll these clips’s speed in code.
Now i find a way,by blendtree .
Anybody have better idea?

Unity 5.1 will have this functionality: Runtime Animator State Properties (speed, mirror, cycleOffset) for 5.1 - Unity Engine - Unity Discussions