I believe the RTD is ground referenced, with approx 2k8 to 3.1V to provide a relatively constant current.
I used a series 33R resistor with a transistor driven by PWM used to bypass the series resistor and a 10uF cap to make a low pass filter.
In this configuration, 100% PWM gives the standard temperature of 260 (or 0 deg offset), it is then nice and linear down to 0% PWM, where you get a -80DegC offset.
In theory, adding a fixed value parallel resistor to the RTD would allow the base temperature to be lowered in order to increase the extrusion temperature above 260DegC, you would then have to compensate with the PWM to get back to a default of 260.
Equally increasing the series resistor value will increase the range.