I just got done doing this with the sweater I am working on now. Exactly as suzeeq says. Just knit in the round until you get to the point where you want to start working the front and back. I keep the necessary number of stitches, usually half, on an extra long circular needle and just continue workinging the front with the circular needle I've been using.
OTN: Jeckyl and Hyde Hat, Shetland Shortwrap( )
FO: Lacey Stole, Library Capelet, Dead Fish Hat, Tree Bark Scarf