Drill the head of the screw off with a 5/32" bit to get it to come through the chassis, then maybe you can get ahold of it w/vicegrips.
Be careful to only drill the screw head, and not the chassis hole itself.
5/32" bit is only a guide, it doesn't have to be 5/32"...It just has to be as thick as the shaft of the screw, so you can get the head to seperate.