Are these carbon fiber heaters? I think as long as you don't cut through the edges you can cut them in the middle, or shorten them if you need to. I think you can cut holes with a punch through them also. I think I'd do it that way and only cut three holes left right and center for the hog rings to go through. Or, you might just do the area behind the listing.
No one lives forever, the trick is creating something that will.