Someone was asking earlier, but yes it's possible to use the gamepad as the screen and use other controllers to play. Girlfriend and I just did the GP to try it out, but it's really hard to make out tracks and turns, especially the antigrav sections, so unless you like frustration, wait til you're familiar with the tracks first.
Initial impressions: Wow, so much harder than any other Mario Kart since Double Dash, which is a good thing. Was trying motion controls, as I never used them in Wii, and I kept having issues turning, but I'm sure that's just me, since some record holders are using the wheel. Can't wait for this weekend.