I would find someone else to cover for you. Or, here's a concept, it's the boss's/owner's problem and they know everyone's schedule better, tell them you are sick and let them find someone else if they want/need to.

However, if you feel you have to find someone and don't have anyone else to find, I'd call the guy recovering from pneumonia -- he's in charge of taking care of his own health and dealing with his family, etc. He may want the extra money after being out sick.