He'll write down, one-time-pad encrypted and in Baseline, four guesses for Wish phrasings that will destroy arbitrary circles of country, along with some half-assed calculations about how to adjust the numerical parameters to destroy different sizes of circle, plus a lot of explanation about what the phrasings mean, the underlying equations implying the existence of antimatter and how to anchor the meaning of those terms in observable reality. Once decrypted, you're going to want a wizard to understand that math and you might be further helped by checking in with Ione Sala if nobody else around understands concepts like electrical charge and quantum spin already.
If that doesn't work, try squeezing a lot of hydrogen together, or conjuring it in tight proximity to itself. Here's three guesses at a Wish phrasing that'll do that...
If that doesn't work, try conjuring a relativistic projectile, careful where it's aimed at, but pointing it towards the center of mass for Golarion seems like it should unambiguously point 'down'...
...Wish phrasing that steers an asteroid into Cheliax, where Keltham has tried to phrase the Wish to put upper bounds on the mass and the impact velocity, but it's not impossible that something like this is what went wrong with the Starstone impact, and Wishes do have a reputation for going wrong, so maybe consider this one something of a very last resort. Probably still better than Cheliax taking over Golarion and becoming a factory for souls going to Hell, though.