Aligning bone's roll accurately to rotated objects I am trying to rig a belt with a lot of things attached to it (small boxes and other accesories). I want to add a bone to each one but the problem is that this accessories are rotated in many different ways and I am not sure about how I should align the bone roll for them. 

In the simplified example I provide below I eyeballed it and the result is somewhat decent, but I want to know a better approach. The center bone is supposed to control the other two bones at the same time (but again, I am not sure about its roll or placement) and the arrows indicate the direction I am looking for, which is more or less the normal X in edit mode.
Riggers usually set the bone roll to have the main movements on the X axis (like in your example, possibly having the main rotation with positive values of X). But if you simply parent the external bones to the central, all 3 bones will rotate on the central bone X axis, which is not what you want. One good approach could be setting two drivers, so that every rotation of the central bone will be reflected by the external bones (on their own axis).