The best way to tie up any of your plants to a steak or trellis is using strips of nylon stockings, pantyhose, tights, whatever you want to call them. The thin stretchy material provides a firm hold, tight knot and doesn't cut into the plant. One pair of stockings makes many ties. So, go through your drawer and grab that pair with the little snag and go tie up your tomatoes!
Don't have any of your own stockings? Ask your Grandma.
Or buy a cheap pair at your local second hand store.