I give you kr_renderOverscan!  It'll render overscan perfectly for the times when your camera needs to line up with other cameras in other applications (such as Nuke).

Just select your camera, run the script and it'll pop up a dialogue box displaying your current resolution height and an empty box below that.  Just input your desired new resolution height into the empty box and let the magic happen.  It'll adjust your post scale automatically and your camera will line up perfectly with the other cameras in the other programs.

Since I use vray at work, I had to include 2 lines of script to change the resolution with vray.  If you don't use vray, just delete the lines:

setAttr "vraySettings.width" $newWidth;

setAttr "vraySettings.height" $newHeight;