“Perhaps he would say that he was working on his shmiras einayim”
I’m not sure why shmiras einayim should be a problem regarding his wife, but that gave me a good idea.
He could say, “Chanala, you are so attractive, and that dress is stunning on you! Since it looks so good on you, I am concerned that it could pose a problem if you were to wear it outside. How about if you just wear it at home, and I’ll give you money to buy another dress that you can wear outside?”