Prying and wiggling enough usually gets pesky rivets out. Its not fast or pretty, but if you have more time than money like me...
If you get a big adjustable wrench from the garage, you can use it kinda like a vice to manipulate the thin sheet steel. Try that if you run into a roadblock. If its particularly stubborn and wont de-attach, just smash it flat and shove it forward. And leave it there in the front of the case. I did that once and it worked fine.