New version - see post below.
Light wrap is a pretty standard procedure for blending a foreground and a background layer together. It exist in every compositing application that I know of, except After Effects. However, it's possible to create your own, and this script does it with a single click. It's based on a technique described in Mark Christiansens book "After Effects CS4 Studio Techniques, plus a couple of enhancements.
To use it, select you foreground layer and you background layer(s) and run the script. It will create a new lightWrap composition, expression link the transform propertys, and give you a slider control in your master composition to set the amount of bluriness of your light wrap. Adjust blurriness and opacity to where it looks good. But remember to keep it subtle! Usually I lower the opacity to somewhere around 10, 20%.