Slice and Dice
Having tried both the freezing and heating methods on these Kingston RAM modules, I can say kudos to Kingston; you really have stuck these things on tight!
I'm going to resort to the slicing method to remove these heat spreaders. The first thing to do is find some suitable wedging tools. If you have a Swiss Army knife then use the toothpick; this should give you an idea of what you should look for as well. Now, most heat spreaders are different in some subtle ways, so it's up to you to judge what you need to lift up the spreader just slightly.
Once you have your wedge, slide it into an edge to get some lift going, and then carefully use the knife to slice away at the exposed thermal pad. Craft knives and Swiss-card knives are excellent for this as they have thin blades.
Once the first chip is done, insert your wedge a little more and do the next one.
Take care not to damage or chip off any of the tiny surface-mount components on the PCB, because that means INSTANT DEATH for the RAM.
Once you have done one half of the RAM, leave your first wedge in and find a second one, then start again from the other side. Soon you will have an entire face of the heat spreader off!
Repeat the above for the opposite side.
Once you have sliced off the adhesive (or alternately used the heating or freezing method with success), now begins the clean up operation.
Using your thumb or finger, gently start peeling the gunk off the chips. If you have available some acetone (nail polish remover), then apply liberally to the gunk on the pads to help dissolve the adhesive. This is also good if the thermal gunk was a liquid epoxy; it should help break down the adhesive nature of it.
Keep at it for a while until you have removed all of the gunk from the surface of the chips. Don't worry too much about the stuff on the sides, so long as the tops of each chip are clean where your new heat spreaders will stick to, that is fine.