After you posted this, I tried a bunch of starting moves to see if any of them would work. I finally gave up and tried the revoltingly cheesy option of putting Froslass on my team. The game randomly picks where to put each 'mon on your team in the puzzle. It took several tries but I eventually got a usable "break" on the initial setup and was able to make a good/lucky enough first move to finish it off.
I consider this a highly disappointing and unsatisfying way to S-rank this puzzle. If someone can figure out how to make a team without Froslass and bring down this puzzle in one move, I'd love to hear about it. That would be the elegant solution. Of course, it might not exist. Froslass might be the only option. Bleh.