It should be as simple as calling transmitBegin(), do your send() series and then transmitEnd(). With dummy data, I've been successful with it (see the OOKTransmitTest example). You might need to use setPowerLevel() to lower the RF output power if your receiver is very close (during testing). You posted nice scope shots about the process, it should work with the original receiver, too. However the receiver might use rolling code, some changing bits as flags you need to mimic in your transmitter, etc. What kind of receiver do you have?