You are talking about the North Bridge cooler. As far as I know, its perfectly feasable. As I said, dont apply too much (so it squeezes out of the sides). Only enough so there is a very thin layer. One last tip, after re-reading what you posted earlier in this thread (re. chip goo/heatsink compound that was supplied with something), you might want to buy some higher quality compound to ensure correct and efficient transmission of heat to the heatsink.
Arctic Silver 5 is aparently very good whilst
Cooler Master High Performance is more mid-market.
There is an alternative with thermal pads, however they are thicker and tricky to apply