I wouldn't suggest lying or hiding it. You only do that if you are afraid or dishonest. If you made a deal or gave your word keep it. Sometimes it's just better to say what you are doing and do it.
However, ease yourself and your wife into it. Maybe it a trip to the B&M or an afternoon with your friends. That is kinda what happened with me.
If you can, get her involved. Use the time you are smoking to hang out with her. That really helped with me and my wife. We would sit outside for an hour together. No kids. Just chatting and smoking. Of couse now that it is turning colder, I've moved the basement. My company, if not my wife, is the CS chat room.