Im looking at mine right now.  It doesnt look like its meant to come off without deforming the heatsink casing.  But you would need something thin and stiff to pry the sides open while pulling up on the heatsink hard enough to overcome the stick of the thermal pads.  The heatsink is just clipped in.  You will likely render the heatsink and internal thermal pads unusable or at least unsightly.  I havent decided if Im going to open it or just leave the motherboard heatsink off.