I am pretty sure i know the answer but i think i will ask anyway. In FCP7 you could create custom canvas resolutions for projects that are going on a varity of displays (monitor walls, projector, screens ect.) I am currently working on a video element that will be projected using DL.3 Lighting Instrument at 1648x472. Am I out of luck when using Avid MC 6 or is there a super secret way that i am unaware of?
You could make a 1920x1080 canvas in photoshop and create a 1648x472 "videosafe" overlay, start a 1920x1080 project in Avid and drop it on the top video track at 50% opacity. Cut your piece and keep the important stuff inside the overlay, then export to After Effects and render out the final movie there.
And if you're not familiar with Avid, here's a nice keyboard shortcut (I hope I'm remembering this right) - Alt+Ctrl+Y. It will open a dialogue box asking what track number you want to make. I'd make the video track for the overly V10 or something - it won't automatically make the other nine video tracks either, keeping your timeline manageable. If you need another video track just hit Ctrl+Y and it will add V2, V3, V4, etc... until it hits V10. Lets add 9 video tracks until you hit the overlay.