Yeah I first heard about using the methode on beer on the Maltose Falcons page. When I did it myself, I found you don't actually need a solvent for the dry ice (they used acetone). I had a metal tube that held the bottles upright. Put a flat chunk of dry ice in the bottom of the tube, then insert bottle so the crown is resting evenly on the dry ice slab. Set your timer for 2 minutes. When the timer goes off, the yeast plug will be perfectly frozen. Your timing may vary, but 2 minutes was the sweet spot for me.
I also tried using everclear as the solvent, but that didn't work very well at all. even after 5 minutes in the brine the plug wasn't totally frozen. If the core of the plug isn't properly frozen, the procedure will be botched. It's really easy to freeze everything except for a tiny hole in the middle, so if you try this, have a dental pick or something similar on hand to fish out the plug.
It's also easier to use a bench capper to press the plastic cork in, rather than a rubber mallet.