I don't think you can
although the individual companies are always a few pennies cheaper. I presume you're using the old "two singles rather than a return" trick? The only other way I know is to split a journey down - often 3 singles (say EDI-NEW NEW-YORK YORK-KING X) is cheaper than one EDI-KINGS X. But it's a massive fucking faff to save not much and you don't get the same seat all the way.
( the mighty badger Aphrodite, on a bar stool, by your side, Fri 4 Nov 2011, 16:31, Reply)