Yeah we used to setup zip wires in caves with just normal caving rope.. which is static (doesnt stretch) and given a bit of intuition with bungee cords like Callum does then that seems like the normal sort of thing to do.
Dont know if you've seen this yet, but this is how the collective do it:

Looks like theyre either using dynamic rope and the stretch to slow it down, or setting static up between trees with a bit of play in it so that it sags with the weight of the person attached to it.. stopping/slowing your impact with the tree at the other end!