No single game will do it, but a load of unique and appealing exclusives to Wii U would.
That doesn't mean Nintendo buying up 3rd party exclusivity, assuming major players in the gaming market can be bought like that, selling exclusivity can have a damaging effect to their reputation and the big guns won't do that unless it does something more than just gets them a load of money, they need it to have a positive effect on their overall public image.
More like Nintendo either needs to develop games internally, building new studios, using existing Nintendo owned devs to make new games or they partner up with lesser known external studios that have yet to make a name for themselves, because that will be way more appealing to the overall games community, it basically shows that Nintendo really cares about giving something back.
In order to get 3rd party, Nintendo should have built a system that is seen as a viable option to sell a good chunk of those publisher's games.
Exclusivity of 3rd party games isn't needed to get huge hardware sales from 3rd party games, you just need to have the most appealing platform for those titles as far as the 3rd party audience is concerned.
The best thing Nintendo can do is focus on making a big, compelling and quality library, using their existing library of IPs and making new ones, that provides an equal level of variety as Playstation (I always say Sony's variety is why they have been as successful in gamers eyes all these years) and quality that appeals to every kind of gamer.
Focus on one element in the market and neglecting any of the others will always lose you millions of potential customers.
