Launch an external app or website for incoming calls - Ignore Internal

I have configured the settings to pass the incoming phone number as a parameter and launch a search in our CRM via URL string. This works great AS LONG AS it was a direct incoming call and not a WARM TRANSFER. Our prior phone system (Mitel) ignored internal calls for their CRM screen pop url string. How can I set this to ignore internal calls from other extensions and only trigger AFTER the call has been transferred?