Joann, in your situation you'd be better off pruning the roots of the plants, and that is is you have some fruit that is nearly as large as its gonna get, nearly full size. This will shock the plant into going into the ripening stage but yet won't kill it.
The smaller fruit will also begin to ripen so you'll get small ripe tomatoes but that is better than none at all, eh?
Normally the first frost is not a hard one so you could also cover your plants with a row cover keeping the frost from nipping the leaves. Oftentimes the first frost will be followed by another period of time of warmer weather so if that is the case that will give you even more time to get some goodies off those plants.
Hope this is helpful.
Happy Gardening...
Shoe
