the fuel cell is up above the rear axle, you would have to drop the rear axle to do any work on the fuel cell..
The book answer is to remove the exhaust from the Cat Converter back, then remove Panhard bar, sway bar, and shocks while supporting rear axle with jack. Lower rear end, remove fuel tank, remove replace pump. The simpler method is to cut a trap door in the rear hatch area. Google camaro fuel pump trap door for detailed instructions.