The halacha is not that he has to work – it is that he has to make sure that his family has a parnassah. As long as the family has a parnassah (and he did not do anything assur to obtain that parnassah), he has fulfilled his obligation.
If for example, he is independently wealthy, he does not have to work. Likewise, if his wife wants to work and she earns enough money for the family, he does not have to work. On the other hand, he would not be allowed to tell her that she has to work. Of course, if he feels that it is in the family’s best interest that she work in order to support him in kollel (or for some other reason), he can certainly discuss it with her as long as he does so in an appropriate way.