I wrapped the zip tie around the back of the fish, where it is mounted to the wall, and through the hanger on the fish extender. Then either cut it off or wrap the extra around the back of the fish. It worked well and you couldn't really see the tie.
As far as gifts, we were on the 11 night med cruise and had 27 rooms participating in the fish extender gift swap. Some ideas were custom pens with our cruise logo and cruise date. (see July 28, 2007 Rome...ancing the mouse, on the meet board), a deck of disney playing cards, magnets and pins with our logo but you could also use any Disney character, postcards from hometowns or ports of call, a small package of pasta picked up at one of the ports, A small bag of "pirate" things including stickers and pencils etc.., glow sticks, candy, key rings, pads of paper, sticky notes, mardi gras type necklaces, a british flag, dice, and lanyards.
It was great fun to check the fish extender as we returned to our room. You never knew what would be in the pockets waiting for you.