I believe this is close to the other rq of having multiple flights under same number (ie same flight on diff. days assigned to diff. planes but under same number). Which will require some changes and at the same time it would be good to consider the whole scheduling thing more.
I'm not sure how this would interface with the current system and of course there will be naysayers who claim that it's not realistic, but perhaps you can create a flight (number 123) to be flown for a single day and simply add an extra box indicating "create 7 daily flights". The day selected (let's call it Wed) would then be flight number 123A, Thurs would be 123B, Friday would be 123C etc. Then, when it comes to scheduling the flights to aircraft, you could have another button to "select all A flights", "select all B flights" etc. since all of the ABCDEFG flights would be sequential. After this, on the destinations list, the flight would be listed as one entry instead of 7 with a little icon or something to denote its a 7 day scheduling scheme.