Is there a way to wire a digital display into a thermistor input to read the value of that thermistor?
Many digital panel meter modules will work at 5 V power supply, and probably won't take much power, so that you might draw that from the thermostat. 

But these are no good. They will measure voltage, but don't take the non-linear characteristic nor the offset into account. You'll need a microcontroller to convert the voltage input to a temperature reading which then can be displayed.  

Most microcontrollers have ADCs (Analog-to-Digital Converters) to read the analog voltage of the thermistor, and convert it to a digital value the controller can work with. You'll need to know the characteristic of the thermistor and its series resistor to know which voltage agrees with which temperature. You can use a mathematical formula for that, or a lookup table.  

If you use a microcontroller with an on-chip LCD driver you can directly connect a display like this one, and you won't need anything else; just the microcontroller and the display. TI's MSP430 controllers are very low power, and so is the display, so you'll be able to run it of the thermostat's power supply.