yeah -- you just keep flipping the needles over, just like you would on straight needles.
The main advantage of doing wide pieces on a circular needle is that you don't need 2 REALLY LONG straight needles, you just need 1 kinda-long circular needle and the work rests on the big wire in the middle.
Does that make sense?
(PS -- be warned: once you start using circulars, you'll get addicted. I don't buy straight needles anymore)