After reading through the links in my previous post, I added a 1/8 stereo normally closed headphone jack that is connected to the PPM output of the remote's microcontroller and the PPM input of the remote's radio transmitter. Since the jack is normally closed, I should be able to remove the headphone plug from the jack and the remote control will work normally.
First, I cut the trace between pin 20 of EM78P458 and surface mount resistor. I then soldered a wire to pin 20 and another wire to the resistor. In the picture you'll notice that, I ended up soldering the second wire to the spot between the resistor and cap. Alas, I'm not an soldering expert, the wire I used was too thick and the pad on the left side of the resistor lifted. I ended up adding a 1k resistor to the circuit to correct this.
I ended up putting the jack on the right side of the antenna so that when used, it would stay out of the way.
The mod looks really clean and I works like I thought it would. Without anything plugged in, the remote works like it did out of the box!