Reverse anim sync group

How possible reverse synchronization for some animations in anim “sync group” in state machine?
For example: i have forward and backward walk animations, all this anims set to “can be leader” in sync settings, on 0.25 point of forw anim, backward should be on 0.75, ( or 0.37 - forw, 0.63 - back ), synchonization time shoild be reversed. This need for perfect transition blending between this anims.
Sorry for my english.