"Short of..." indeed. You already know the answer, although it doesn't need to be general; it only needs to work on a single codebase.

A recent and highly relevant example is the migration of the TypeScript compiler to Go. They did not use an LLM to translate the code. Instead, they used LLM assistance to write a deterministic TypeScript-to-Go translator and then used that to translate the code. I have far more confidence in this approach than in letting the LLMs rip on the translation itself.