The main idea behind the counter balance notion is to be able to mess with the speed down the line, perhaps by having a can that could have sand added or taken out.
The bungee has been used here quite succesfully at a number of shoots and is worth looking into. You might have to check the strength of the bungee, too much bounce could be as bad as slamming to a dead stop.
Alternatively, a line with a suitable degree of elasticity might work just as well.
If you ever get over here in the summer, Carol Edwards runs a mad two day shoot called "Jim's Jungle Jaunt" at Shackleford near Guildford in Surrey. The targets are all eccentric homemade cut out animals made by her dad Jim and the woods are only shot in once a year, so it is quite dense in parts, with ferns head high.
Nobody in their right mind would go for the prizes or medals, but if you like a little chaotic fun, it's just the ticket.
The flying gibbon is notorious. You stand on a hillside in the ferns and look at a dark hole in the foliage. Each group gets one look at the gibbon flying past this hole before turns are taken to call loose and take the fleeting shot opportunity. All the misses, of which there are plenty, are easy enough to retrieve since they wind up in the leaf mould on opposite side of the gulley floor.
Rod.