There are a few options depending on your room, projector, and the screen.
If your room is long enough and your projector can be moved back(farther from the screen) and zoomed to still fit the screen..that can help spread and weaken that bright center to make it a lot less noticeable. I don't know how far back you'll be able to go and still fit the screen, but every little bit helps.
If the screen is in decent shape, it might be worth a decent chunk of change depending on the brand. You might consider selling it and picking up a screen with neutral or nearly neutral gain. These not only look great in dark rooms, but also tend to cost the least because they are more simple to make.
If the screen is bothering you enough and is either in poor shape, not worth much money or you simply feel like selling would be a hassle, you could always paint it a neutral flat white or very light grey. That'll fix the hotspot no problem, but is only a last resort.
It is surprisingly easy in most cases and can even be done with a simple paint-roller using interior flat wall paint.
Dimming the projector (possible to dim further with an NDfilter) can help somewhat, but usually will just make both the bright spot AND the dimmer surround darker..so it'll still have a spot in the middle.
Last edited by Ftoast; 07-27-2014 at 06:01 AM.