I don't see a problem with the saw. Dull the edges first and cut away, slowly. The snapping tool might work too if you can follow the contour and get close enough to the edges. My first inclination would be just to forget about cutting them down and drink more wine if you want more bottoms. If you have a recycling bin in your area, you can pull bottles from there. I brew beer and that's how I got all my bottles.