A way to 'digitalize' a wheatstone bridge
Quote from the wikipedia article on wheatstone bridges: 


  Alternatively, if R1, R2, R3, are known but R 2 is not adjustable, the
  voltage difference across or current flow through the meter can be
  used to calculate the value of Rx, using Kirchhoff's circuit laws.
  This setup is frequently used in strain gauge and resistance
  thermometer measurements, as it is usually faster to read a voltage
  level off a meter than to adjust a resistance to zero the voltage.


So it sounds like your best bet is to just measure the current of your wheatstone bridge digitally. If you adjust R2 until the current is very small, then you can use a large value shunt resistor and detect extremely small changes in current.