Mod Ideas/Sunshadow
Description
The idea is that all player and actor shadows on the map, change angle based on which way the sunlight actors on the map are facing, more then 1 sunlight actor makes more shadows.
Simple
Interested Scripters
inio (as part of Sourced Player Shadows)
Discussion
Foxpaw: Sourced Player Shadows is essentially what you just described.
inio: The version currently in the works even has explicit support for sunlights, and even fades the shadow in and out based on occlusion so you can have complex (but large scale) objects shadowing into the map and not have to make highly detailed shadow volumes to make it work.