How to Get the 'Vamp Eyer' Achievement in Metal Gear Solid 2: Sons of Liberty HD

I've played through Metal Gear Solid 2 at least fifteen times now. Easily. But I have never seen or heard about this Easter egg. So consider my mind blown when I tell you that Vamp (who should be dead three times at this point) is in the final cutscene of the game.

During Raiden and Snake's monologue after sword fighting the President of the United States, Raiden will take off his dog tags and proclaim that he'll make his own identity. Right around then, if you zoom in at the right area, Vamp will be seen glaring at you.