It CAN be done.
Last year I booked MAN-LHR-JFK return in F with my wife - she thought we were flying Y. We managed to do the MAN-LHR dom sector and get to the doors of the CCR without her knowing. Do OLCI. Use a post-it note at baggage drop to make sure they do not say anything. Keep hold of the tickets and with a bit of luck, you'll do it.
The look my wife's face when I pointed at the famous CCR room door and then said, 'Come on let's go in..' will live with me forever.
Good luck and enjoy