With the Playstation Store I believe you can actually purchase PSN titles from your PC for the PSP (and possibly PS3? I forget). I've googled but I can't quite tell if there's such a service for the Wii U store.
There's a Wii U downloadable title I'd like, as it's on sale, but I don't have a Wii U yet. Is there some way I can purchase the game (even if I have to download it on the title, just "claiming" it would be super) without the console itself?
Currently you can't, Nintendo ties the download with the console, not with the User ID.
Update since the answer has changed. Unlike three years ago, you can now buy titles on Nintendo's website, and they will email you a download code. You can save this code and enter it in on a Wii U console at any time later to download the game. The same system applies to 3DS.
Nintendo Support link on giving games as gifts (though you can also just use the code yourself).
There is also another option. If you create a Nintendo Network ID, (hereafter NNID), you can register a download with your NNID, and can download it whenever you want, as long as the game is still being distributed. You must have a NNID, and it must be connected to a Nintendo Account (I believe).
