There is no airflow around the south bridge - it's under the speaker box. I know the drilling was awful :-) - I used an 800 Watts power drill with 1.6mm drill

There is no airflow around the south bridge - it's under the speaker box. I know the drilling was awful :-) - I used an 800 Watts power drill with 1.6mm drill bits (that thing fits 14mm bits!), didn't have anything else. In the end it works fine. A sheet and a mesh is a good idea, but it would take too much work and the heat transfer would be impacted - I specifically drilled the holes so that the copper sheet is cooled by incoming air, therefore acting like an additional (large) fin for the heatsink.