Some ideas - The best if possible: get the circuit to output your desired baud rate.
Assuming that its already been built and that your RF channel cannot accommodate such a low data rate, get a microcontroller, such as the Atmel ATTINY2313, which has one UART -use that UART to send your higher speed output data in a standard format, and then use a firmware UART to receive your nonstandard (about 150 baud) input code. If there is no handshaking between the gizmo that generates the approx 150 baud stream and the RF link, then it would be really simple.