Sorry I know this is an old post, but I think to resolve your issue you want to set the trunk destination to be the fqdn of the vcs-c. Simply changing from IP to FQDN actually makes the difference you're looking for. Just make sure you CUCM can query DNS. That will cover the domain portion of the caller-id being sent from CUCM to VCS.
Also under the outbound calls section of the trunk you then have the option to set the host portion of the caller-id to be DN or URI.