Your idea is valid, but there is a flaw- the design and placement of the light(s) being used. Most rear lights these days (at least the more powerful ones) tend to be a bit too 'focused' of a beam. Once you get the light properly aimed and then move your head/torso, the light is no longer as effective.

One way to increase the effectiveness is to use multiple lights. Fire Eyes and the B&M Topfire are some examples. Using a powerful seat post or rack mounted light combined with one of the above product (or similar) could provide some decent coverage.