When looking into using CGI composited in live footage I thought back to the recent idents that had been made for the 3 sky channels. The same footage is used for each but with the CGI aspect different depending on the channel. This gives each channel its individuality while still tying all them together. They have used the programs they show as themes as well as standard footage in the background. All the ads revolve around the idea of the number of the channel breaking up in some kind, which really creates focus on the number itself therefore completing its job.
This is much like the technique used in Zombieland which has been proven in both of these that it is a very effective method creating focus and drawing the eye in a composition. The key is to get them to look like they are in the surroundings as opposed to just stuck on after. For example the numbers need to look as if they are sat on the floor rather than floading in the space. this means that lighting and shadows will have to be used in conjunction with the numbers when compositing with the live footage.