I would actualy try to encourage third parties to either make their own exclusive core games, or at least core multiplatforms.
One way I would do it would be with "free advertising", in addition to other ways of advertising:
Say, nintendo puts a banner with ads of existent and upcoming games on wiiu on a very visible place on the OS. This banner will be always visible and change everytime users go into the OS, the catch is that nintendo will decide which games to be featured on the banner, this way nintendo can reward third party studios/pubs who put their top/quality games on wiiu, studios wouldnt have to pay anything for this marketing move.
The game can be casual or hardcore, as long nintendo deems it important or of high quality, also developer "behavior" on the console could be taken into consideration for this program (devs who port or make games very often for the console, indie devs attempting a new ip or exclusive game, whatever).
Lastly, the banner would analyse the games, demos, and trailers that the user plays or watches and update accordingly (a similar code is already used on the nintendo channel for searching/rating games), nintendo would only have to update the system adding the game data and depending on the tastes of the user he/she would see the adds of their preffered game types.
Clicking on the banner for a game will open a window where users can see details, reviews, official trailers, user gameplay videos, download a demo (if available), buy/rent/preorder it, and anything else.
Actualy I hope they do this anyway for any game too, but it could be a way to get these devs more on nintendo's side, since one of the biggest gripes of third parties is their perceived small performance of their games on nintendo consoles.
There are plenty of other alternatives, like paying devs/studios for any reason they have for skipping a wiiu sku. If the reason is technical, but still within the realm of possibility, then nintendo may as well try to find a way to help these devs to make the porting/developing possible.
It is quite unfair that nintendo would have to do things like these when ms and sony dont need to, but maybe it could be done to lay down the foundations for future generations of steady support.
Still, I think doing anything to get certain third parties on board no matter HOW will be better than doing nothing and letting only casual and nintendo games sell millions. The Miiverse, NinNet, and the recent partnerships are definitely hints of forward thinking and encouragement from nintendo.
(I realise my idea is pretty much already done on the nintendo channel, but it would be more complete, it would be always visible in the OS and with access to all the info in just one click. Also I dont know how nintendo manages third party advertising on e-shop or nintendo channel)