How to play animation reversely with animator component

I am working with unity 5.0, and I use animator component to control my player. I want to play an attack animation reversely, is there any way to achieve this?
I know it can be achieved with animation component, but I can’t use it.
It seems that I could change animator.speed to -1, but It has some conditions and I don’t know how to do it.

Unity 5.1 apparently implemented the options to change the speed of a single state during runtime. I am currently planning to try it out myself, here is the link to the Dev post announcing the new features:

Runtime Animator State Properties (speed, mirror, cycleOffset) for 5.1