Like illmatic416 said, you can open up the phone and bend the little springy clip upwards a bit, and that will give the slide more "snap" when you open and close the phone. It does nothing, however, for the side to side play the slide has.
The only way I can see to fix the side to side play is to shim the rails the slide, uh, slides inside. Maybe use some very thin pieces of aluminum or spring steel or something?