Do NOT try reversing the airflow...you stand an excellent chance of frying the CPU...the heatsink you have is NOT designed to be used the way you suggest.
Dallas Don's suggestion of raising the fan off the heatsink with a spacer is a good one. also drilling a blowhole directly over the Cpu in the side of the case with a case fan drawing air in from the side down to the heatsink fan is also a good way to get cooler air directly to the heatsink.