I think we'd have to target someone with a decent resume as an OC who's also flamed out already as a head coach at least once.
Just for example: Pat Shurmur. I wouldn't be super excited for him, but he's done reasonable well as an OC while never having a QB of Allen's caliber. But he's already flamed out TWICE as a HC, which combined with his age makes him very unlikely to get another shot even if the offense here is lights out.