Seems that there is a special shim being made for Athlon MP processors, and Cooler Guys is making them. Head on over to Iamnotageek.com and see what they have to say about the Cooler Guys Athlon MP Shim. here's a snip:
"Shims are nothing new but this is the first Athlon MP shim I yet to see. It is available from the Cooler Guys. For those of you who are unfamiliar with shims they are designed to prevent your core from being damaged when installing or removing a heatsink. They do this by creating a level surface with the core, this prevents the heatsink from rocking to one side or the other and from chip away at the edges of the core."