The H31 is a little brighter then the 4805 so that would help with your lighting. You could also build a screen with blackout cloth and a wooden frame. You then just paint the cloth (actually you paint the vinyl side) with any numerous paints (check avsforum for the differen types of paints)...
I know this is kind of going the other way with it but is there any chance you could get a PJ? There is nothing smaller then a pj and a screen. If you can control the light it might be worth considering. Even if your are only 8 feet away from the screen you could still do a 55" diag screen...