Firstly, I can see no particular purpose in using a "sensor shield". All it does, is to give you male pins to connect to instead of the female pin headers on the Arduino proper.
The problem with multiplexing is that even if you limit the segment current to say 10 mA (330 ohm resistors on each segment)
Analog pins are digital pins. It just happens you can if you need to, read analog voltages on them with the appropriate instruction.