I think I like Regus's answer better. Take a resistance reading of the thermistor at freezer temperature and then another reading a 35 degrees. The difference will be the ohm value of the resistor you would need. You could also use a potentiometer to adjust the resistance. Once you get it dialed in, take a resistance reading of the pot and use the same value resistor on the rest of the freezers. Resistors are cheap, you would be saving your customer a lot of money.