Inspired by the BB philosophy some time ago (think it may have been the high-voltage test to destruction) I did just this some time ago.
Mine is a single 100mm fan blowing out through a rosette not half as nice as the one BB did.
My fan is a $10 el cheapo however, and it has expired.
Ths makes the situation
much worse, as the normal airflow path is now short-circuited.
This results in overheating of HDD and video card.
I have solved the problem as follows:
On starting the computer I check the wall-mounted thermometer.
If it reads above 24 degrees, I remove the side of the case and place my desk fan on the floor next to it, blowing directly into the case.
If the room temp goes above 26, I turn the desk fan onto its High speed setting.
When flying small prop planes, I turn the sound off as there is sufficient noise from the fan to (more than) compensate
Edit: do not try this at home unless you are about to upgrade your entire system
