Quanon

You could use a AuroraDlight, give it some "big" values in its settings and it'll pretty much act as a sun. Though I'dd use lightmaps to enhance the feel in your area. T'is a ton of extra work though. I've been messing around with a plugin in for 3Ds Max that streamlines teh whole lightmap business, but it isn't FREE.

And I haven't seriously tested it out in the game itself.