You can accomplish this by 'intercepting' the initial call.  I.e. digits dialed that would normally route to the orginal target are routed to your application CTI route point.  The app can then paly messages, gather digits and otherwise make a decision to route the call further.  By capturing the original called number, you can easily redirect the call to its original intended destination on 'green light.'

Downsides to this mechanism are fairly obvious: the app is 'in the way' of every call to this destination (scalability/impact,) and handling app failure scenarios may be tricky, in order to ensure some level of service.