Variable Bit Rate (VBR) encoding will dynamically switch up and down the encoding rate based on the data it is given and will form an average over time of the final encoding rate specified. If you make the simple realization that more data requires a higher bit rate, you can fake out the codec using some tricks giving a little more quality to problem areas (sometimes at the expense of others, though). In essence this is faking a higher bit rate in spots...but inreality it is lowering it overall (keep in mind some things work backwards).
Add a few seconds of silence or pure black to the beginning and end of a wave or video file. Don't add too much or you will sit around waiting needlessly on the end product to do something. The key here is PURE. If the silence is noisy, that noise must be encoded. If the the pure video color is blocky and noisy, that noise must be encoded. Encoding noise is a waste of bits and will not gain you anything. In reality you can use any pure color in the video, but black is the most common.
In the Middle. If you're really good you may be able to add a little here and there in the middle regions. This can really only be done during transisions (like commercial breaks, before and after the open/close). If you add too much, it can really throw off the timing and feel, though.
A main limitation of this method is that it really should be very near the section that needs the extra bits. This isn't always doable. The main application for this is pure black at the beginning of a video that fades in (about 1 second should do). I've noticed many videos break up really bad like that at the beginning.
This method could be described as loading up the bit bucket...but it isn't free. (Some may call this reforcing an average bit rate at specific points.) If you are rendering to a specific file size, this will eat up some extra space and will average down other points in the video to meet the final size requirement. Depending on the video and other settings, this may or may not be noticable. The trade off for the extra bits in the bucket may even pay off on other scenes down the line, though. Since this is an advanced technique, it is more of an art.