Well seeing as there is a passive heatsink on your NB presently, you could slap on an active heatsink if you are really that concerned about temps. What is your actual temp? Why do you think it is so hot? Are there any overclocks? voltage increases?
Northbridge temps can easily go up to the 50-60 degree mark, don't worry too much if its up there, although having a small fan or an aftermarket chipset cooler would definitely help.
If you can place an 80mm or 90mm blowing cool air on northbridge heatsink then it would significantly lower the temperature. I have the same problem before and so I put an 80mm fan on top of my graphics card and aimed towards the n/b cooler. The temperature went down big time and it is not hot anymore, reading 35c.
Or you can get active coolers like the Thermalright HR-05 chipset cooler. This thing is huge and can be mounted with 80mm fan for a much better cooling.
First make sure this cooler can be mounted in your system. As I have mentioned it, this chipset cooler is huge and can be block with other hardware and or cpu cooler.
How do you know your northbridge is too hot. i have the same motherboard and i agree that my northbridge is way too hot to touch. i,however, overclock my pd 830 to 3.6 without increasing the voltage on air. The system is completely stable for two prime 95 instances for over 10 hours but the nb is very hot. In fact, i took off the chipset cover and reapply the thermal paste, but it is still hot. I guess , that is the way it is with the passive cooling. I think it is ok because i have been using this setting for over a year and the system is going strong.