Basically my idea is to place a small housing piece of rubber or some material that will provide grip and stretchability.
This housing piece will have a hole in the middle for something I decided to just call a rivet piece, which will expand and secure the housing piece sideways as to grasp only onto the plug.
Now, you can attach this cord a variety of ways, but I figured if you place a piece of line through the housing so that once the "Rivet" piece is placed it it secures the line along with it.
I made this Paint picture which is really sketchy, seeing as I came up with this idea like half an hour ago, but I hope this picture helps build some visualization.

So it's a pretty basic drawing and idea, The hardest part of this tension tool would be coming up with the supplies that worked well, just a little experimenting and i'm sure this will work nicely.
What do you guys think?