Is it really necessary for you to be able to tweek the gain of your instrumentation amplifier? It seems to me you just need to select a precision resistor that gives you the gain you need for the maximum signal level that doesn't exceed your ADC input range. Use the instrumentation amp's gain equation to get the actual gain that results from the value of the gain resistor you actually use.
I imagine you are balancing the transducer at zero pressure in software. I don't think you've talked about how you intend to calibrate it. Maybe the data sheet span voltage is good enough for your application, or maybe the transducer comes with a calibration sheet.