Hell, that by itself might scare the shit out of the North. A mandatory and orderly evacuation of Seoul, with a few aircraft carrier groups parked off the North Korean coast, would put them in a position of "shit or cut bait." I realize that it's almost impossible, but to treat it as a drill, get people to pack their belongings, and then suddenly have it not be a drill and implemented, would be a very strong message. Obviously, you can't do it for long (1-2 days MAXIMUM), so the North either takes the message or you then hit them, hard and with everything you have.
ἡ δὲ κἀκ τριῶν τρυπημάτων ἐργαζομένη ἐνεκάλει τῇ φύσει, δυσφορουμένη, ὅτι δὴ μὴ καὶ τοὺς τιτθοὺς αὐτῇ εὐρύτερον ἢ νῦν εἰσι τρυπώη, ὅπως καὶ ἄλλην ἐνταῦθα μίξιν ἐπιτεχνᾶσθαι δυνατὴ εἴη. – Procopius
Ummaka qinnassa nīk!
*MySmiley*