It depends on how you intend to deliver. If DVD, Blu-ray or broadcast, it won't work. Those formats all have fixed resolutions that must be adhered to. The only two methods for creating a 'blank spot' in those formats would be to crop off part of the image, or to reduce the size of the image, which would create 'black' on all four sides, not just the bottom.
The only way you can do this would be for computer playback, where resolutions can be anything you want them to be. Essentially you'd create a new sequence with the extra pixels, and just keep your clips at the top of the frame. (Do create a sequence whose dimensions are both evenly divisible by 8, though.)