Victim said:Split the full action into 2 parts. IIRC, there's an option to "finish full round action" as a partial. So the hostage taker grabs a helpless guy, and starts the action. Then he readies an action to finish the coup de grace.
I like that. You could consider the "grab him by the throat" bit to be starting the CdG, and the "slash the throat open" bit to be finishing it.