If you still have green tomatoes at the end of the season, stick them in a paper bag with a banana and that should help them along. In the greenhouse, stop feeding the tomato plants and cut back on watering, which should quicken the ripening time.
Take the tops off cucumber plants and nip off the tips of the sideshoots a few weeks before you want to remove the plants from the greenhouse, to coax them into swelling. Remove any leaves that look dusty, as this could be the start of mildew.
Peppers and aubergines are also sensitive to temperature at night and are unlikely to develop further fruits at this stage, so focus on what you have by cutting down on watering and feeding and closing the ventilation earlier on in the day to trap the heat inside. Even if you end up with undersized fruits, they will be edible.