Can you maybe explain better what motion it is you are trying to get?.
The reason I ask is because you mention that you want to bind X and Z position to the pelvis. I assume X and Z for the root bone to follow the pelvis. Currently the root bone will follow on X and Y. So I’m not 100% sure of what it is you want to do there in stead, because the root bone X axis already will follow the pelvis. Do you also want Z axis of the root bone to follow on the pelvis?. I guess, I’ll ask this, do you want all 3 axis of the root bone to follow the pelvis?.. or am I missing the point?.