What I use is a lemon. Yes, just threat the lemon onto the rotisserie rod to the position where the chicken will be. Make sure that you have one fork on the rod. Place it pointing towards the middle on the handle end of the rod. The lemon will fill up the cavity of the chicken and help hold it in place. As the chicken cooks the chicken will shrink a little giving it a better hold. Of course if you don't like the lemon flavor on your chicken you can use something else. Try an apple, onion, or even a potato. Of course the potato is going to be harder to get onto the rod, but the neutral flavor won't affect the flavor of the chicken as much (if that's what you are after). Just try to pick something that will fill the cavity of the chicken.

