You should be able to declare the thermistor as a temperature_sensor ( Configuration reference - Klipper documentation ) temporarily using something like a “Generic 3950” thermistor definition. Then heat the sensor to a set temperature and run the QUERY_ADC command (see the docs for details - G-Codes - Klipper documentation ). That can report a resistance, which you can then use in configuring an actual custom thermistor for the sensor ( Configuration reference - Klipper documentation ).
-Kevin