aspect ratio.. creating the cinematic 2.39:1 rectangle

Im trying to make a nice wide, cinematic aspect ratio picture ... shot with wide angle lens in "letterbox format" .. set my sequence to 720x480 anamorphic but the picture is still not wide enough, so I enlarged the picture so it would fit out to the ends but then I lose too much at the top and bottom, so I tried changing the sequence settings to like 700 x 480 but then FCP wants to re-render everything. is there an easier way to get the cinematic wide look? more then 16:9 I think its 2.39:1 thats what Im after.... in FCP.. I will render out to HD at the end.

any ideas how to do this without having to re-render before editing?

WiseGuyProductions.ca