[fowlerm]

I was looking at the transmitter over the weekend and found out the same thing. It may be possible to use a PIC or a basic stamp to take the serial output from a computer and use generate the appropriate PWM pulse for the desired analog value. The only thing that you would really need to find out is what the timing is for the different PWM outputs. The pinout for the tether port (for those of you that are interested) is from right to left if you are looking at the port on the transmitter is:

1 - Tether detect - used to enable/disable the radio transmitter
2 - Gnd
3 - PWM output
4 - +5v