I don't know exactly how easy this would be to do, but if it's as easy as I figure, it might be worth it since it's just a minor thing. NWN lets you start with maps already revealed as is usually used in towns or other areas not worth of selfexploration, how about letting Upper Sanctuary natives start with the Upper Sanctuary map revealed to them and Lowers having the Lower Sanctuary?

Of course, the ones starting in the Underdark or a prelude can not profit from anything like this.

Shouldn't be difficult to add, but I'll let somebody else decide if it's worth it!