it is sensitve matter to me, when he applied EE if he is not married then it is ok to add you after got ITA.. otherwise.. he got points to get ITA bcoz of he didn't add you. I don't think so he can add you now.. thing is there is no edit mode available in EE to add you. So he should add you by sending additional family member form and I doubt they may accept. If you don't want to take chance, better wait to get PR and ask him to sponser..
This is my person opinion only..