We have this, so we pick the tomatoes and put them in the fruit bowl with/on bananas. As user58258 says, its the gas that bananas emit that cause all fruit to ripen (ethene if I remember correctly). So you need it to surround the tomatoes to get them to ripen
I've put a few bananas in the greenhouse to no avail. I've got 50 odd tomatos to ripen I'd need a skip to ripen them all off the vine !!