Just the other day I read an interesting presentation from Midway, documenting their work on "Mortal Kombat vs. DC Universe". In it, they describe the various rendering tricks and engine changes they used to get Unreal Engine 3 running at 60Hz. One such trick that peaked my interest was how they approximate specular lighting.
Basically, they just treat the eye vector like a directional light, and use it to calculate lighting like normal. Then, they multiply the result by the current ambient color/intensity. This approach gives them specular highlights that are cheap, always visible, and look like they are influenced by the environment.
This is especially convenient because the equation reuses calculations from other parts of the shader. It uses NdotE that was calculated for rim-lighting, and ambient lighting calculated from SH. So it produces a passable approximation to specular lighting that fits in well with environment lighting, and doesn't require having actual lights present.