I just plain suggest not opening the bottom case other than the user servicable part too. There are so many fragile compnents in there, that if you do not line up the bottom and top cases correcly when putting it back together, you have a "not-worth-it" chance of ruining a component or hurting a cable. Also, the heat transfering issue too should be enough to stop you there.
I was a service tech, quitting just recently to go back to college, but if you don't have the Apple service stuff to do it, don't even waste your time. Have them do it, or BTO it that way, even the bottom slot too, max it all out when you get it.