Are you sure what you're up against with booting up a new Mac in a store? They all have that intial new user start-up ritual. Can you quickly bypass that? Just not sure. Historically, to get to the normal desktop, you first must have to register the computer, as that set-up stuff. Only after that can you test the speakers, the display, etc. At least that my gut response.
Nope, no way to bypass. I open the box at the Genius Bar, use their power supply, and start up. Then, I go through the setup ritual. I can start over when I get home, if I need to. I also bring a flash drive with Pixel Check on it for the display tests.
edit: I believe I cancel the registration part, even tho it make you fill out everything.