I'm looking at the skeleton that came with Poser 4 (don't know if it's still in 
the newer versions) and the clavicle and scapula are one piece.   
It should be possible to separate them out using either a modelling app
or the Grouping tool in Poser, but that would require re-rigging the whole
thing.   

Hmm.  One trick that wouldn't require re-rigging:  

Use the Grouping tool.  Start by locating the lCollar in the grouping tool.
Then pick New Group, name it lClavicle, and carefully select the clavicle.   
(This is the hard part!)

Then do two things with this group:
Assign Material so you can hide it on the real figure; 
and Create Prop to make a new free-floating prop from the clavicle.  
Then parent the clavicle prop to the sternum,
and make the material of the real clavicle invisible.

Do the same on the right side, and save the figure with the props attached.

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