OP asks about installing 2012 to USB, specifically saying he doesn't want to install it from USB..... Gets 2 replies telling him how to install from USB.
I'm not sure it would be possible, or even sane to be honest. It's not designed to be an embedded type OS - it's one thing running something like ESXi from USB as you don't lose much if the USB stick dies and you don't need the capacity.
It begs the question......why?