resizing for dual-monitor

[Becvar]

I use 2 monitors, with the viewport reduced to keep the playable area of wow on one monitor, with the remainder black (typically for inventory, quest tracking, atlasloot display, etc. The resolution selected ingame is NOT the resolution of my display as a result (game selects 800x600, while I'm actually running a playable area of 1440x900 and a total wow window of 2480x900.) Is there a way to change the nUI display to conform to the shape (1.6 aspect widescreen) of the main monitor ONLY?