I have 3 bones (in the same armature) a sword, a sheath and a hand
So I put 2 constraint (childOf) to the bone of the sword. One, attached to the bone of the sheath and the other to the hand. Now, if I move the bone of the sword (in pose mode) to the hand and set the reverse, the influence of the 2nd constraint will also change the position in a maner that the sword can't come back in place in the Sheath.
That sounds really simple but I have no clue how am I suppose to do that :\