Objects selectively receive shadows

Hey guys! Working on a new game and i have a question about some buildings i have made, and receiving shadows. Basically i have objects flying around the environment that i want to cast shadows on my buildings. However i have lightmapped my buildings, and don't want unity's lights to cast shadows on them. Ie: buildings receive shadows from objects, but not from the light itself. Tried culling masks on the light, and its not working correctly. Anyone have a script i can use to selectively receive shadows based on a layer list, or something to that effect?

Cheers! Jon