I don't think CBR addresses anything beyond individual payload locations of the message body.
I have no experience with object paths, but in your case you should be able to configure an alternate
payload location with the "standard" action property get-payload-location, e.g.,
<action name="route-message" class="org.jboss.soa.esb.actions.ContentBasedRouter">
<property name="get-payload-location" value="my-payload-location"/>
This property and the corresponding property set-payload-location is a convention in most of the ESB library
actions, and works here also.