Hammer? Seriously, if you honestly couldn't care less about the case.
Why not a wide flat head screw driver? Why not? Again, if this thing is destined for the dumpster anyway, right?
I have 3 compact Macs. The case on all of them is so tight that I cannot get it off with any manner of shaking. I therefore use the poor-man's Mac cracker which came with one of these Macs I bought off EBAY. I don't really like it that much, but it works. It consists of two thin pieces of metal, both of which are bent at an angle at one end. Put them back to back and then insert in the case gap, then wedge open slightly. I do this in 4 sections of the case, a few millimeters on each section, and then the case loosens enough to slide off.