If you know the address, go to your Place tab in FTM or mapquest, enter the address and get at least two cross streets (one on either side of the address you have). Then when you go to the 1940 census search, go to "already know the cross streets?" Fill in the blanks and it should narrow your search down to one district, or at least make it easier than what you had before. It will still require page by page search, but not as much. Hope this helps.