The other day, as I was working on some baby socks for our new grand daughter due on Valentine’s Day, I caught myself pulling the cord of my circle needle around the corner as I started the transition to the back needle tip, of my Magic loop. I do this to prevent ladders, where the cords of my 47 inch circle needle form loops on each side. The trick is to pull your cord through long enough so that you can bring it to the left under the left needle tip, then swing it down and around and up over the top to start the first purl stitch of the last section of the round. That is why I always opt for the 47 inch cord.
Here you see cord being pulled to the left and under the needle. This move takes the stress off the gap between the left needle tip and the cord.
The right tip of the needle is then brought around and over the top, then inserted under the yarn in preparation to be purled.
Once the stitch is purled, I make sure to release it, allowing the right hand needle to lie parallel to the stitches riding on the cord to the right. If need be, I take up any slack.
In the above photo, you can observe how I accomplish this on the knit side. Here again, I swing my cord around to the left and secure it with my thumb before knitting the next stitch.
Once the new stitch is complete I allow the right needle to lie parallel to the cord, then take up any slack that remains before proceeding to the next stitch.
In both cases I continue holding the cord around the corner for a few more stitches before releasing it to finish my round.
Just passing it on!!
KT
Creative Knitting - Beyond Knit and Purl 
Thank you very much for these images! I am just learning how to use the magic loop and purling at the start of a needle/row was making me crazy! Your photo above (#3) was just what I needed!
So glad it was helpful.
KT
May I just say that this is the only technique that has worked for me with magic loop. Have tried youtube videos and countless techniques. Before this mega laddersville Now nice smooth stitches. Thank you thank you thank you.
You are most welcome. It is nice to know that someone was helped with this post.
KT
Thanks for the pictures. I’m a left handed knitter and I have 40″cord but I figured out how to do it from the pictures
Yet another knitter who’s grateful for this tip: Your post from 2013 solved my 2018 two-at-a-time (TAAT) sock problem! Thank you for sharing your discovery or creation.