Sanogo could possibly do the job tbh. I think last game showed Giroud's main importance was that he provides the focal point. He holds the ball up, and brings others into play with his little flicks and what not. If you've got Sanogo with Sanchez Ozil Walcott (back soon right?) behind, plus Ramsay's goalscoring. If he can bring them into the game you've got plenty of goals to come from behind him.
Is pretty crazy you have this problem in a summer where Balo, Lukaku, Mandzukic have all been available. That considered and the fact Wenger has bought Sanchez for that kind of money and played him there, perhaps he'll simply persist with the plan.