The weird thing is that WAS working, but I covered it up and it STILL worked.
It might have just been a noisy signal or other interference lulling you into believing that it was working....
To connect it for reading variable voltages is easy. Just place a resistor between the photodiode output and gnd. the connection to the analog pin should come from between the photodiode output and the resistor. You could use a potentiometer instead of a resistor so you can vary the output.
If you find the output is too low like this, you might have to use a transistor too but I think that photoresistor has an internal amplifier.
You can do the sums to find the best resistor for the job but a general 1k2 resistor should give you some resolution of results. A potentiometer again would let you manually calibrate the output.