This should be possible with slightly modified (software-wise) Kindle 3 or 4 + Raspberry Pi + Wi-Fi dongle.
I can take care of the software changes, hardware changes involve connecting buttons/switches to GPIO pins of Raspberry Pi.
This solution requires Wi-Fi connection but no wires are needed between Kindle and Raspberry.
Alternatively you can connect Raspberry and Kindle with a USB cable and establish a USB network.
Details:
GPIO input change (detected by polling /sys/class/gpio/gpioN/value) would trigger sending command
echo "send 109" > /proc/keypad (Page Up) or
echo "send 104" > /proc/keypad (Page Down ) over SSH/Wi-Fi to Kindle.
See
https://developer.ridgerun.com/wiki/...e_GPIO_signals