Blender bone world positions

No.525446 ViewReplyOriginalReport
Lets say I have two bones, A "Root" bone and a "Child" bone, the "Child" bone has the "Root" bone set as its parent. How can I make it keep its world position while the parent moves?
Now, the reason I ask is because I want to create some "root motion" animations for UE4 (which I have gotten working) but since the root bone moves during the animation, its really hard(or as far as i can see; impossible) to keep the IK targets I use in the same place while the "Root" bone moves.
As an example see webm-related(by me): (I'm aware that this animation is horrible for root motion and in this case it won't be used)
But in that rig I have the head as the root bone, when it bobs up and down I'd still like to be able to keep the IK targets located at the feet still without bobbing with the head bone!
Any suggestions on how to do this? The easiest thing would obviously be if I could copy the world position of a bone and then paste it on the next keyframe, but I can't for the life of me find that sort of functionality!
Now another important aspect is that i can have only ONE root bone and the root bone HAS to be animated. Using the "child of" constraint doesn't work for this reason as the "child" in that case is not an actual hierarchical child to the "parent".
(All these constraints are put on me by UE4, one of the biggest engines out there)

Asked this everywhere, nobody knows. Why is Blender this stunted? It feels like its basic functionality that they decided to leave out and instead made fancier loading bars.