A BO is not the same as a decrease, even though it decreases the stitch number. At the beg of the row BO 3 sts, that will get you into the cable sts, so you might as well just k2tog then and knit the rest of the cables stitches. You probably won't be binding off on a cable row, and if it should be one, just don't do it, don't cross the sts. Then it won't pucker up there.
sue- knitting heretic