If you feel the top of your CPU block in a well set up and adequate loop it will just be a little warmer then room ambient. Like Duckie was saying the heat is being moved to the rad to be dissipated.
I always point a fan at my CPU block, can't hurt even if it doesn't help much. But really designing and building a HSF CPU block wouldn't be worth the cost and effort, I wouldn't think.
You would be better off optimizing your rad/fan set up. Really thats the main tweak left in WC'ing, rad and fans, over rad a little and put as high a CFM fans as yo can stand on it.
But it doesn't hurt to try if you would like to, hey a C is a C, when your topped out on your OC from heat throttle a C cooler temp can be a lot. That can be the difference in getting that last 50-100Mhz CPU-Z.