When I started reading your post, I was a little confused, because knitting on circs is supposed to get you a big circle.
Then I realized that you want to knit straight on circ, right?
When you get to the end of the row, don't continue knitting. Turn the whole thing around so the working yarn is on the left point and the purl side is facing you. The bring the other point around and start knitting. Just keep flipping the whole thing over as if it were on straights, but use the other end as your 'other needle'. I hope this is clear enough.