You can turn on RECORD A CALL TONES in system flags.
You can make the system play a "I'm going to start recording now" message: create a new system greeting, select it (day and night) for the record-a-call app, and be sure to turn on PLAY PRE-RECORD-A-CALL flag in system flags. Works great, automatically, soon as button is pressed but DOES NOT appear on the recording.