I came back to this thread to do exactly what beacher suggested -- report in.
Neither of the suggestions worked, so I asked, "What if we take another CD and push it in just far enough to push the 'stuck' CD back just a bit?" Guess what? The "stuck" CD popped right out!
However, any CD we now try to insert gets pulled in only about halfway, and then spits out. This leads me to believe the drive has a mechanical problem.
New question: How hard is it to replace a combo (CDRW/DVD) drive in an iMac?
P.S. It's a "snow" egg-shaped iMac, not a flat-panel machine.