You can change the corners from square to different degrees of round, even on Chris' oblique lines. Just right click on the line, choose
Format>Line... and select a corner rounding style.
You might also take a look at
VSD Grafx shapes at Visio Cafe, especially the "Essentials" stencil. Their isometric lines are nicely curved and, therefore, more "cable like". Be sure to use the yellow and green adjustment handles to change the contour of the lines. They still aren't just like the cables in your diagram above but it's another free alternative.