I am not so keen on elastic rope (it is heavier than dyneema) and much of the problem of stretch can be overcome by caternary cutting the silnylon or using fabrics with very low stretch such as tyvek or cuben fibre, but nonetheless this method of keeping your tent taut is worth sharing: http://gossamergear.com/wp/diy-self-tensioning-guy-lines-2 A sprung tip on my tent pole ( I use a one-pole set-up) would have the same effect with less trouble. May work on this.
