I think killing off one roller and keeping the other one head bound or asleep or etc. would work. Luckily, I remembered that he was weak to volt from the original Etrian Odyssey, and also that volt was generally the spell that the fewest enemies resisted, so I had like 3 points in it. Simon's poison skill also helped, and I have him using the Hexer grimoire, so he was able to remove the curoller buff. I almost killed Cern the first time on Expert, but it was just so annoying, and I had to use a lot of Nectars.

The Highlander is boring. If I can't create a character completely on my own, I would much rather have a hero with a strong personality than some dull halfway point.