okay as started in the water cooler here is the whole kit and kaboodle...

I. shoot normal 4x3.
you could shoot letterboxed, but this will be a bit narrower so if you can makeshift a cinema format matte or safe area for your monitor...do so.

II. start a custom project with a frame size of 720x304
if you've never done custom project... don't know what to tell ya.

III. import the video.
yes it's squashed...DO NOT:maintain aspect ratio.

IV. drop "image pan"
set the size to width:720 and height:304
now use keyframes and move the frame around as you like it. frame it your way, frame it your way.

V. export
i'd export uncompressed with a frame size of 720x304 and then you can start a new project, import that clip, maintain aspect ratio, and export out a letterboxed version.

here's a sample. i'm using the clip from my feature...

http://theater.suntropolis.com/scene117-cinescope.html