you explain it to the masses in a big press conference as to why you should spend $300+ on one. Show off 3-4 demos of AAA first party exclusives and keep it moving.
I'll tell you what you DON'T do tho:
Stick it in a corner and expect people to flock to it when you got sony and microsoft coming in swinging with better hardware. The Wii U is not selling well, people have no faith in the system so Nintendo thinking that they can just "show up" and expect people to flock to it during THIS e3 is ridiculous. Nintendo Direct is not the answer either.
Do you realize that Nintendo is basically turning away 1000+ websites that cover these things during the events and they really expect a bulk of those visitors to watch Nintendo Direct?