The only way I can think of would be to set up a CRA, delete the greetings, leave default timeout of hangup, create a phantom, forward all calls to new CRA, set up secondary extension key in place of SPCL, set secondary extension to phantom that's forwarded to CRA... While on a call, you'll press that "cancel" button, which will transfer the call to a phantom that's forwarded to a hangup. Not really practical since you'll still have to hangup to complete the transfer...