Well, your PSU may or may or may not have a fan on the top (since thats how the P180 works) mine has it on the back, so I need not worry (Smart Power 2.0 500W)
I'd say you can do it, so long as you don't choke the PSU's airflow. Since the nature of PSUs is running hot, cutting off the airflow could cause damage do the components, as the FETs won't have their heat dissipated, and the heat will build up....and that can damage all the ICs, FETs Cpacitors and whatnot.
Try pulling wires up and stuffing them in the area where that little compartment for screws and whatnot is, that's were all my excess wiring is hidden.