Originally Posted by
pinniped
MCI+2000 is effectively a contiguous-48-states (plus most of Canada) search.
I tested it out: MCI+2000 to LON, one-week stay, all of July. (I figure this whole idea of using other airports is mainly useful when DTW-LHR fares are likely to be very high.)
This is a good idea! OP's question is a good one though, and one I have thought of many times. It would be interesting of one of the more computer inclined among us could develop a page that allowed this.