If you look closely at a Crystal Orb or a Blue Orb you will notice that the fan is built into a heat sink of its own. Mounting one of these onto an already existing heat sink wont do you much good. I would just mount an open fan to it. If you get a fan thats the same size as the heat sink your refering to, then just put a drop of superglue on each of the four corners and set it on there. It should work just fine, infact I have read here somewhere that others have done this with good success.
Good Luck!
Lvcoyote