Will "Burned in" textures work for you? I've tried using the shadow shader and they say you can edit the shader to get different results - but I tried it and gave up. Perhaps I'm weak - but the bigger drawback (than the strange shadows) was the STRAIN it caused to my framerates. I chopped that out real quick as framerates dove.
Baked in textures would probably be your best bet. That's how they got the look they did in the DarkGDK samples download - the program called "World" (Its a small "level" consisting of a few closely knit buildings you can walk in and around (and fly))
I write in code (sometimes)!=(always)