I was thinking about elastic components in guylines a few days ago. It occurred to me that the ends of a bit of bungee could be spliced into a braided guyline at two points, and the unspliced loop of guyline could be coiled around the exposed bit of the bungee.
The piece in the photos is 1/8" urethane core, dacron sheath bungee spliced into 500lb test, 8-strand braided Vectran line. In this example, the exposed part of the bungee is about 4" long, and stretches to about 6.5". This is similar to the latex tubing method except in this case the guyline coils around the elastic component rather than within it. I wonder if this method might be a little lighter than the latex tubing approach.
I also wondered if this might be more durable than the latex tubing method because the UV-sensitive elastic material is protected. It also occurred to me that, in contrast to the latex tubing method, this design can't abruptly bottom out. The guyline coils straighten and constrict the stretching bungee, and as the bungee reaches maximal stretch, the guyline and bungee strain against eachother to achieve straightness under the load. Under very high loads (I tied it to a beam and dangled from it), the guyline becomes nearly straight, and the bungee coils around the guyline (the opposite of the resting arrangement). Under my bouncing body weight the guyline never becomes perfectly straight.
One of the shortcomings of this design is that the braided guyline must be able to splice over the bungee. I wasn't able to get 1/8" bungee into braided lines smaller than 400lb test. So, this forces you to use unnecessarily robust guyline. If you use dyneema, the absolute weight penalty of the larger line is not very great, though.