I would think the rartionale for permitting SEs and EPs to have lounge entry when they are not flying is just this situation: where you have a friend, relative or colleague who is flying (AC or CP) you are not, but you would like to host them to "your club" prior to their departure. What other reason is there for having such a privilege: hey, let's go down to the MLL for a coupl'a free beers..."? (Sorry, too much ice cream and sunshine on Canada Day, I got carried away.)

Would you not go back to the service desk where you were abused last time and now that they have been re-informed of the rules, they will give you a gate pass? As noted, your friend will already be able to clear security with their boarding pass, then it is on as your guest to the MLL.

Now this to me is the logical, common sense explanation. But you are, afterall, dealing with Air Canada and I suppose various staff could interpret things quite differently. And if the terminal and MLL is particularly crowded, they might invoke that as a reason to deny entry to your guest.

Good luck this time.