Dont do that, it will screw up the p180s airflow design... Sucking out the hot air is much more efficient than mixing the hot air with cooler air. THe 180 is designed with a nice airflow in mind.
You can add an extra fan into the p180 for the graphics card but only if you really need it. So far I havent found a need.
PS: Flipping that fan should increase your overall temperature by quite a few degress, in one of my smaller boxes I did it and the results were dramatic (like 15deg C) and resulted in a very noisy machine.