In a bad late-blight year, tomatoes often get infected just as the first fruits ripen. All you can do is pull the plants up and save all ripe and mature green fruit that look healthy. These tomatoes can be spread out in a warm, dry spot to ripen fully. But this is often a waste of time as it is very likely that fruit are already infected and that they will rot before they ripen. Don't despair! We have worked out a simple method to cure infected fruit, that is, to kill off the blight pathogen without damaging the tomato. See The Organic Grower, 11, Winter/Spring 2010, p31: No more green tomato chutney: how to cure blighted tomato fruit.
Essentially, green fruit with latent blight infection was incubated at 40C for at least 12h, then ripened at room temperature. Control fruit rotted before ripening but blight was eliminated from the treated fruit. Small quantities of fruit are easily treated in a chicken-egg incubator and some domestic ovens can be set to hold 40C (104F). An alternative is to use a water bath (fish tank?) and put fruit in polythene bags.
Higher temperatures for shorter times might be effective but tomato fruit might suffer some damage.