This is a photo of the receiver that I have. Bigger...

For completeness, I'm including a photo of the label on the back of the receiver as well. Bigger...

My receiver has 4 little tabs holding the top and bottom halves together. After cutting through the labels on the sides, I found that you could very gently push on the tabs through the holes in order to separate the top and bottom of the case. Bigger...

Here we see the top removed. Notice that there is an extra row of locations to plug pins into above the two channels of pins already present. Bigger...

Ah Ha. Pay dirt. The surface mount chip in the top right is an HEF40175B chip, which is a quadruple D type flip flop, which can be arranged to look like a shift register. Sure enough, the signal lines on the two servo outputs which are present go directly to the output of the D-flops. In fact, the unpopulated pins appear to be for a 3rd channel. Bigger...

So, I cut the trace leading to the extra signal line. You can see the cut just above the top-right of the HEF40175B. The output was originally connected to pin 2. I determined that a nearby resistor was connected directly to pin 9 (the clock) so I then added a piece of blue wire wrap wire from that resistor to the unused channel pin. Bigger...

Here you can see I soldered in an extra pin into the "unused" channel. By adding an extra pin, I was still able to use the receiver in it's original form. Bigger...

I added an extra hole in the case to get at the new pin. I was orignally going to make a bigger slot for all 3 pins and decided in the end to just use one. Bigger...