Hmm I saw a nifty trick I think it was on bit tech. I searched for it but I couldnt find it. Ill try and explain what they did but its pretty hard to explain without looking at the picture.
Take the abit metal ring off. Now cut the circle ring at the joints at both sides where it meets the clip. What you should have left is a perfect circle wich you throw away, and the 2 long brackets wich go on under the hooks.
drill a hole through the 2 long brackets you have left (the ones that go under the hooks in the center. Now you mount the block on the nothbridge and use like a old pentium 1 clip across the top and screw it into the 2 side brackets that ckip under the hooks.
oh my, I better find the picture. Ill look for it for you. Its very elegant and you dont have to drill through the motherboard or anything. all your doing is cutting the ring but using the existing hook locks from the ring and using a cross bracer over the top of the block and screwing it into the old ring bracket wich in turn goes into the hooks.