I got this pro-tip during a sock competition years ago (can’t remember if it was Sock Madness or Tour de Sock) and figured now was a good time to share it with you, since I’m about to release a Very Cabled sock pattern!
I use this technique for cables that involves 4 or more stitches.
The technique is: add a yarnover in the middle of the cable stitches on the round/row BEFORE you work the cable. Then, when it’s time to work the cable, drop the YO and let the slack be distributed across the cable stitches, making them easier to work.
This is an approximate science, so putting the YO close to the center for cables with an uneven number of stitches works fine. For really massive cables (I once knit a cowl with a 6/6 cross) I might add two yarnovers!
One thing to note - adding slack like this makes the cable stitches easier to knit into, but doesn’t make the finished fabric that much looser. So still plan to size up however you normally do to ensure the FO fits.
I made a video demonstrating this method, which you can check out here: