Sorry but you do need a GamePad, as there's no way to bypass the initial setup (syncing/creating a Mii character/Nintendo Network ID), and unfortunately Nintendo's Online Store doesn't sell the GamePad separately, just bundled with a refurbished Wii U console.
But it still might be worth giving a call to Nintendo's 1-800-255-3700 (6 am ~ 7 pm Pacific, everyday) Customer Service number, or use their webform to see if you could purchase a GamePad from them.