Happened to me once last year, I ran into a friend at YYZ and brought him into the MLL. The person at the counter told me that she shouldn't let me in becasue we weren't booked on the same flight, but that she would do it "this time". Checked the T&C's when I got home and realized that this was specifically allowed. I almost always carry a printout of the T&C with me nowadays for situations like this.