Why not just fill it up to MAX as normal and just give the customer a 1 l bottle of oil to put in the boot.
I'm with you mate, though I wouldn't say band-aid solution, I'd say a bulltish solution, but i'm a pessimist when it comes to service departments

Overfill the car, say it's normal which contradicts everything the manual says about oil level, tell the customer it's fine in regards to the catalytic converter which again, contradicts the manual....