There is no direct or simple method to assign thermal conductivity based on location. Thermal conductivity is a material property. It must be associated with a material id number which is assigned as an element attribute. You might be able to write a macro that loops through the entire model one element at a time and perform the following steps.
Find the element centroid
Find the thermal conductivity at that location
Assign unique mat id number for each element
Create a set of material properties for each mat id
This approach will result in a complicated model with many matids but it might work as you intend to use