an idea ive been tossing around im my head is to feed an PWM signal to the ch 5 switch. on/off/on/off. if its slow enough for the AVR to read (250us starting?) but still faster than the servo can respond it might work.
you might just end up frezseeing the servo, i dont really know. it would depend on how the servo reacts to quicly changing signal. this might work better on an analog servo.
edit: if this did work, you would also end up constanyl moving ur servo, they might burn out or live a short life