Penny still going strong approaching two years now.

Liked Juan's solution but being lazy, figured it was too much trouble. A penny seemed to be just the right thickness so researched the copper content of pennies in different years. Grabbed one from the 70s which was in the 97 percent range, and used a generous amount of thermal paste to fill in the gaps on both sides of the penny. So far so good. Can watch movies without the fan blasting or the machine shutting down.