How about duplicating the backlight switching transistor setup? The current drawn by the base of a transistor like that is measured in microamps. I guess that would constitute amplifying the signal as suggested above.
So, the "digital pin 9" connection would go to your VSS signal, the "LED Power" (collector) connection would go to the 'duino input pin, and keep the 5V connection (emitter).
I suppose a pull-down resistor would be wise... 10K or so, T'd into the wire between the transistor and 'duino, the other lead of the resistor going to ground.