Not entirely sure what you are trying to achieve. If Symposium/CC6 is controlling the call routing on the CDN then a CTI application cannot also control it, it's either one or the other.
There is certainly a DISCONNECT command that can be executed in a cll routing script, but is does exactly what it says, i.e. it disconnects the call at source which will be the Meridian/CS1000 so the call is no longer present for any other application to take over control.