For awhile I've been hoping that someone would come out with a plugin that uses masking and lightening to fill in shadow areas. And a few days ago I stumbled upon one called Shadow Control.
I only tested it on three pictures. For the tests I compared it with standard methods such as: luminosity mask, invert, fill gray, color dodge or luminosity mask, invert, levels or curves. Both with and without blurring the mask. I also tried it against a contrast mask on one of the pictures.
Bottom line, it worked much better on one picture, a little better on another, and worse on the third. I think this is actually a pretty good start considering that no plugin works in every situation. But you check it out and see what you think.
They also have other plugins there: Highlight Control, Photographic Filters, and Smart Sharpen. Each plugin is $34.95, with discounts for buying more than one. I've only tested Shadow Control. http://www.chromasoftware.com/