I would experiment - I don't think anything is set in stone as to when
analogReference(INTERNAL);
or
analogReference(EXTERNAL); // ??
is called - maybe just a time thing to let the voltages settle before taking a reading.
Apply a 1/2 volt, write a little code to change back & forth, see what happens.
Even if you just use a gain of 10 to get your signal to 1V, you could use the 1.1V internal reference, and then 1 bit would represent 0.1075mV for your display.