As a developer of some search engine for the Amadeus (one of the major companies who provides the air-tickets search), I can say:
Yes, you can, but you should find the site working with Amadeus and provides such option to the search. This option is not as popular as flexible-dates-feature, but you still can try to search such sites. I'll do my best to find them.

As a developer of some search engine for the Amadeus (one of the major companies who provides the air-tickets search), I can say:
Yes, you can, but you should find the site working with Amadeus and provides such option to the search. This option is not as popular as flexible-dates-feature, but you still can try to search such sites. I'll do my best to find them:

• http://uk.bestfares.amadeus.net/ - use the "Add nearby airports" checkbox and "Customs" menu.
• http://www.kayak.com/flights - the same menu, because the search engine is provided by Amadeus