What I did when I transferred my old Alpha from my C400 to my C566 was use some adhesive foam I had left over from my pelitier setup. It wasn't too difficult to balance the heatsink once I applied a small cutout square of foam to the bottom of each corner of the heatsink where it would sit on the chip since the foam compresses pretty easily. The gap between the heatsink and the surface of the chip is almost paper thin so you'll have to trim down the foam quite closely. Then shine a light through the gap with a flashlight to make sure the heatsink it firmly sitting flat on the core.