I have this cable inside a groove on a tool plate, inbetween the wire and the toolplate (not all around just bottom) i wanted to add thermal paste and run a simulation

idk how to add the paste ( or if i even can)

i tried contact sets but it selects one piece at a time and selects the entire wire surface 

is there any way to simulate a thermal paste contact between the two? or add a paste substance to the assembly?