I think the initial idea wont work. Because there wont be any load the resistance might not actually show a decrease in voltage. So here what is currently being tested
Hook up 8 different resistance to the 8 pins of a 4x4 key pad. Wire 4 of the row or column pins to 5v supply directly and the rest 4 in parallel to an analog input and measure voltage / compare it to preset values. if we ensure that the resistance values don't add up to similar combinations, then we might even be able to avoid multiple presses. Will keep this updated.
Cheers,
Pracas