Non-Newtonian models in COMSOL

HI,

I am re-posting this as I didn't receive a lot of attention last time. I have only seen Carreau and PowerLaw models for non-Newtonian flows in COMSOL. However, I want to implement a different constitutive relation of my own that involves some constants and has it's own unique functional form in the CFD module for non-Newtonian flow! The independent variable is still shear rate (gamma dot) but it is a different function than Carreau.

Does anyone how to define this function and then how to call it for calculation of the viscosity for a non-Newtonian flow simulation?