Hello Mads,
If you fill the 17 point curve for your sensor this will allow for an extended range over the pre-calculated flash tables. You will find these settings in the "Inputs->Coolant sensor curve" menu in VemsTune.
A better (or easier alternative) would be to change the current CLT sensor for one which is meant to measure over a broader temperature range while still being a normal NTC.
Best regards, Dave