Stripped screw head on back cover

Help! I am trying to replace the battery on my Macbook Pro 13 Unibody Mid 2009 battery. I was successful on removing all of the screws except 1 on the top left corner (its a longer screw). I tried many different screw drivers including Phillips #00. It won't budge and now I think I stripped the screw head!! Its so tight there is no way I can get pliers/tweezers or anything to loosen it. What can I do to get that screw out now that it's stripped???