If you can boot into ANY game, you might be able to launch the bluebomb exploit. So even if on the latest firmware or if you don't have a disc with an update on it, you may be able to recover.
By default bluebomb is loaded from the system menu, but I think it might be able to be loaded via a game as well, I'm just not certain if small tweaks to the procedure and/or "stage" code would be necessary.
Edit: I didn't see the post above until just now, but it's a good sign that many of us are thinking bluebomb could work in this situation