Configuring a trapeze
On a Hobie 16, the bungee which extends under the trampoline and is connected to the trapeze wire on the other side acts as a sort of "preventer" to keep you from doing the grand circle if you plow into a wave with the bow.
Your bungee, if it helps pull you in toward the cockpit, could also act as a preventer to some degree. If you want a more secure line to attach to the rear of the boat temporarily, you could certainly do it.
One feature catamaran trapezes usually have is an adjustment to allow you to effectively vary the length of the trapeze wire. It really helps for visibility (seeing through the window in the sails) and comfort on long hikes. The trap wire has a block or loop on the end through which a short line is run; one end has the dogbone or whatever connector you are hooking up to; the other end has a loop attached to the bungee. In the line towards the bungee loop is a plastic block used to adjust how much line pays out as you hook up and push out from the boat (see diagram in Murray''s catalog page 25:
As you can see, they''ve got fancier systems which allow you to adjust on the fly as well.
If you want to single hand it would be a good idea to set up your boat with a bit of weather helm so it doesn''t sail away from you if you fall off!