I have rigged the bungee a number of ways.... and that's what you should do. Experiment. There is no one "right" way. It will depend on how the sheet leaves the car to the winch as to whether you can get the elastic cord to "automatically" pull the car back. In reality, the multi purchase control line moves the car forward against the upward load of the sheet. Theoretically, that upward load also forces the car aft when you ease the control line. The bungee is "theoretically" there to assist the car's aft movement. But... as you'll learn, it doesn't necessarily work that simply. On the C27, with the car mounted lead block on the genoa track (the outside rail), the sheet will rise dramatically from the lead to the winch. That means there is upward load BEHIND the car also and it is nearly impossible to install enough bungee force to overcome it.
My solution was to extend the sheet straight back to a turning block, which was essentially the old car and jib lead, sending the sheet to the winch at a constant angle... making for better winch operation and providing absolutely no resistance to the car's aft movement. I studied many diagrams of the various equipment manufacturers' systems to understand how to get the shock cord stretch to be effective over the anticipated range of the car's movement.... more important for roller reefing applications than for a fixed sail.
I first tried doubling the cord around a small block anchored to three feet aft... with one leg on the car and the other on the boat. There were inexpensive snap hooks on the block and cord ends. That gave me a long range of motion, but not enough tension... so I played with the attachment locations and eventually got it to work. I also tried simply clipping both ends to the car, doubling the strength but giving up some range... that worked better... but I surmised that if I were roller reefing I'd also need to relocate the rear anchor point to compensate for the range of motion loss. As the years went by, I somehow realized that simply tying a short loop "handle" to the back of the car was very helpful... I could simply pull the car backward by hand!
All of these setups were based on my belief that the upward load on the sheet from car to winch was an impediment to smooth operation. I recently went out and rigged the sheet directly from car to winch, not extending back to the turning block.... and guess what???? I works.... not the bungee, but the handle.. The upward load forward and aft of the car did not affect its ability to move.... as long as you pulled it by hand. It will not work with the bungee though.
Summary... Tie on a loop handle to that eye at the back of the car so you can sail and enjoy the awesome advantage the EZ glide system gives you right away. Buy about 20 feet of shock cord and a hand full of appropriate size hog rings... 1/4 inch cord for long range movement, thicker size for shorter range, more power. Get some inexpensive bronze hooks and a couple of small mini blocks for doubling. Btw, the doubling means you can use the smaller diameter shock cord and it'll give you more options to experiment with. Then you'll be able to experiment confidently. Have fun.
