Agree with the others - wet lease is a red herring but in my experience any existing itinerary on the same day with less than 8 hours, regardless of whether it is own metal or codeshare, your departure or another, has available seats or not will mean that the free transit is rejected. They are fierce about those rules and there is no room for negotiation I think. If anything, I thought that being on a codeshare excludes you too (but I think that may be of the paid special rate transit).