Mecanim root bone loses animation on y axis

Hiya, i've been looking for a solution for this for a while now (hope I'm not missing something obvious). I animated my my mesh in blender, just a basic run cycle. My problem is that when i import the model into unity the root bones y motion is lost, I assume this is because of the rig being a humanoid base and mecanim taking over the root y position at runtime.

I noticed that i can base the root bones y position off of the feet which sort or fixes the issue ... however it seems that this method forces at least one foot to be on the ground at all time causing an unrealistic bounce. is there a way i can have both feet off the ground at one time and also keep my root bones y motion with a mecanim compatible setup or do i need to switch to the legacy animation system?