yes i agree, silly weight is not an option even though it is possible. I stopped at 100k as i felt the same as ChongW that eventually something would give.
Thus i went back to hyper extentions. Thes can be done fine without a hyper ext-bench/roman chair, simply kneel with your feet behind you locked under a barbell heavy enough to hold you down. then, keeping your knee backs at a right angle point your hands at your temples and lean forward until you form a right angle with your thighs. Try not to push your bum backward as is natural, let the barbell hold the balance of your body.
quick paint diagram
sorry for crap artwork
Thus i went back to hyper extentions. Thes can be done fine without a hyper ext-bench/roman chair, simply kneel with your feet behind you locked under a barbell heavy enough to hold you down. then, keeping your knee backs at a right angle point your hands at your temples and lean forward until you form a right angle with your thighs. Try not to push your bum backward as is natural, let the barbell hold the balance of your body.
quick paint diagram

sorry for crap artwork