Snap an empty to a bone's coordinate, quickest way? I'm doing a ragdoll system with lots of rigidbody constraints. I use empties as constraints, which will be snapped to the location of a bone.

The problem is that my armature has too many bones and I have a lot of empties to snap to. So is there a quick way to snap a empty to a bone's location? 

The possible way I find is to transform snap an empty to a bone's vertex, but somehow the bone's vertex won't be recognized by the snap tool?
I use the procedure described here to parent an Empty to a bone.  For example set the cursor to a location between a characters eyes; I then add an empty between the eyes (Empty.eyes.rig-dz1), parent that to a face bone to track (might also be able to add Copy Location constraint instead?).  I then have another character whose Eyes have an animated Copy Location (target==empty).  So that when it is enabled, eyes will look the other as the other moves.