Oh they be a bitch. You have to pop one clip at a time and wedge something after it pops, so it doesn't pop again.
I tried it with some small screwdrivers but it tends to leave marks in the casing. I'm guessing something plastic to wedge in there would be preferable?
I would try to open it step by step with a screw driver by opening one clip and put something in between the upper and lower case part... This is also on my to do list for my original PAL-SNES-RGB cable
See the holes that are on the opposite side of the tabs? You can stick something in there to bend the taps until they unclip. And as already posted, once you got one side unclipped wedge a credit card between the two case halves.