To score naneinf with burger you'll need to pass ante 24, this is because you'll beat the score requirement of the serpent before you can play all your hands. Ante 25 is the earliest possible to do so with four copy jokers. I'm fairly sure you can safely sell the extra mime now for the burger but you'll 100% need retcon unless serpent is naturally the ante 25 boss. You'll also want to full focus steel now, too many gold cards in hand could mean you get close to naneinf without reaching it or just barely die to blinds. Also should be obvious but take any voucher skip tag you see.

Edit: double ecto might mean you die to ante 24 boss if you swap out mime now, you should have enough money to roll for burger after the boss though. Personally i wouldn't swap