A long time ago I have made a Xpresso setup which makes it possible to render more canvas. This is especially useful when you need more space around your CG footage after applying Lens distortion. You can not just increase the Output Resolution as this also changes the perspective of your rendering. My Xpresso Setup makes more Canvas size and calculates all changes to the Camera FOV and Offset. This way you get a Rendering which fits pixel by pixel the smaller Version.
Helge Maus made this great tutorial about this technique (only german). You can download the CanvassizeCamera here: canvassizecamera.zip