I tried all the things that were suggested (undervolt, apply thermal paste on GPU). I did undervolt my CPU to a stable 1.000V. But when I tried 3DMark06, my ACPI temps (which I'm told reflects my CPU temps) were above the danger zone of 75C, although the CPU temps themselves were fine. At furmark, temps still remained high though (with the GPU at 94C with aircon on, and 99C with aircon off), and this is even with the GPU throttling itself down to avoid overheating. I'm sure it would be even higher if there was no auto throttling.
Maybe I'll buy a notebook cooler and see how that goes...