A voltage controlled resistor is not an easy thing to do and is virtually impossible to achieve a high accuracy. An ADC and digital potentiometer can be used, but the latter is not very accurate. An array of precision resistors switched by relays, controlled by an ADC is your best bet.
There is something called digipots (digital potentiometers).
When combining these with some analog resistors around the right value, you can have actually pretty precise control (with a limited range obviously).
When used over the full resistor value they lack accuracy.
My best bet would also be a current sink.
When used in parallel with some other (resistive) load you can have actually pretty accurate control.
Than being said, may I ask why you need such an high accuracy of reading temperatures?
The reason why I am asking, is because it is extremely difficult to have accurate temperature readings anyway.
From a physical point of view, not from an electrical point of view.
But even the latter ±0.5 degree C (Kelvin) is already very good and moving your probe a few mm or degrees has a more significant impact.
Not to talk about how tight it is connected and if any thermal grease is being used etc.
edit: another idea would be a motorized potentiometer.
But you have to pre calibrate it, or maybe put a little current sense circuit with it.