Would it be possible to use an resistor and capacitor in series to differentiate which switch is pushed? In the same vein as using a resistor and an analog pin. Instead of measuring the voltage you would measure the length of time the capacitor takes to discharge.
Maybe something like this:
I am new to this stuff so I could be completely off my rocker. If R3>>R5 then when the button is pressed C1 should discharge through the digital pin. This should take a consistent time. The time it takes to discharge would give you which button was pressed. (Now that I look at it R1 and R2 might not be needed) Any thoughts? (other than that I am nuts...) 
-Andy