Correct way to use mecanim and AddMixingTransform?

All of the ways I have Googled on how to use AddMixingTransform involve an Animation component. I want to continue to use my Animator component and achieve the same effect. How do you use AddMixingTransform (or something that is like it) with an Animator? I need to have the top half of my characters body play a different animation than the bottom.

Thank you for reading!

I think you need to be looking at layers.