Well, I guess I'm stuck with this GBA SP with a cracked shell and an unscrewable battery cover. It's kind of ironic that the only screw that is not Nintendo proprietary tri-wing screw is the one that's stripped.
And it really sucks because I have this awesome transparent replacement shell. (I like transparent plastic)
Okay, tomorrow I will see if I can remove the screw with a power drill (assuming I can find one).