stainless copper heatsink surprise

If you are talking about the ones with the bottom copper and the fins on top silver colored. Hit it with a torch. or the oven Idea is a great one. the fins are just soldered on to the copper.

If it is the ones where the copper tubes go up through the fins you can use the same methods but, CAUTION, the tubes contain a liquid and it will pop and squirt you like a water gun wear face and eye protection when heating these. NOTE: not a good idea to use the wife's or moms new Toster oven for this