The worse part can be when the PSU sucks air in, rather then blows out and dumps that warm air on the CPU... But in any case, one thing you might try is adding a case fan above the PSU to help exhaust some air from there. Warm air tends to rise, so that's a perfect place to exhaust, assuming your air flow is all front to back...
BTW, do you have any ventilation holes on your case, abovet he PSU? Only consider adding one, if you do... Lets just say I've seen this before, and from a local OEM, who took the time to add a fan, except that the air had no place to go :laugh:
If you don't, and you have the tools, you might add a couple. But with my case, I didn't bother moding the case to allow 2 fans up there for my HD cooler. Some people I knew, themselves knew a guy who ran a machine shop at home... They used him, and for this, I asked him if he'd be willing...