Found this in the westjet forum:
That's funny. I managed to get 10% on WS by just replacing the "5" with a "10".

My cousin in Ontario got discount codes for Air Canada at some Easter event. Apparently you get 10% off domestic travel in Tango with code MQVEFEF1 or 10% off Tango Plus with J3ZUG941. We both tried and it works perfectly (haven't booked anything though). She didn't know anything about travel periods etc.

http://www.flyertalk.com/forum/westj...romo-code.html