Not that I would encourage something so fantastically stupid as Scuba to that depth on a single, but looking at apnea records makes the engineer in me say it is quite possible.
Odds are he could have made it to 480 on a single, but highly unlikely he would have returned to tell you about it.
A trained apnea diver, probably. Joe Diver on a single 80, not so much. It may be possible, but I think the odds would be stacked against them.
Even if they were to free dive to depth, and use the 80 to surface, once they take that first hit of gas the Narcotic effect would probably be overwhelming. If they used a gas that was sufficiently non-narcotic, the 02 content would likely be too low for breathing once they got shallower.
Then there is that whole "once you start breathing compressed gas under pressure and forcing inert gasses into your tissues you'll have to give it time to escape" thing...
But if the engineer in you thinks its possible and decides to test it, be sure someone videos it for the rest of us!