I don't know if this will help you or not, but it might be a helpful read. It has good tips on how to fix up sloppy ribbing (which in essence, is not much different than cabling in that it is knit stitches followed by purl stitches) and she gives some really great tips to help make that transition between knits and purls look as tight and neat as possible. Hope it helps.
http://nonaknits.typepad.com/nonakni...of_braggi.html