Can I specify that analog pins be used for digital output?
Yes.

http://arduino.cc/en/Tutorial/AnalogInputPins states


  The analog pins can be used identically to the digital pins, using the aliases A0 (for analog input 0), A1, etc. For example, the code would look like this to set analog pin 0 to an output, and to set it HIGH:


pinMode(A0, OUTPUT);
digitalWrite(A0, HIGH)


There are several caveats on that page regarding this.