I assume you mean in addition to the fans that currently draw air out of the system or remounting the existing fans?
If you mean in addition to the current setup, i would have them drawing air out, the same as the ones are now. That way both fans are blowing in the same direction, increasing the amount of air being drawn over the heat sinks and thus cooling more.
I wouldnt really recommend blowing air in, unless you are going to cut the plastic fan duct to allow air to exit out the bottom easier. The way it is designed right now it so draw from the bottom of these ducts, through the heat sinks out the fan. If you reverse this, the flow will be effected and probably wont cool as well.
My two cents...
Caster.