I wouldn't try anything too complex, I've got that same case (or very similar, maybe the next model down) lying around in the attic, it was a junker I got from my cousin last year.
The side panel is so thin you can bend it with your bare fingers.
I'd recommend just getting an A4 piece of paper, then using something round, round off the corners of it and cut them off with scissors, the trace around the paper with a dry erase whiteboard marker or chalk, or a pencil (or anything that will come off easily) onto the INSIDE of the case.
Then cut it from the OUTSIDE (because that means any jagged edges will be on the inside) with a good quality dremel with a metal cutting bit. Remember to use safety precautions at all times when working with powertools no matter how big or small they are. Finish it with black glass molding which you can get at any hardware supply store.
Here's a pic so you can see how easilythe side panel bends, you can see that dent on the side there. When I picked it up it actually crushed under its own weight so be careful while handling it.
Hope that helps you.Edited by Reflux - 6/10/11 at 1:33am